Mathematics with Applications In the Management, Natural and Social Sciences (11th Edition)
11th Edition
ISBN: 9780321931078
Author: Margaret L. Lial, Thomas W. Hungerford, John P. Holcomb, Bernadette Mullins
Publisher: PEARSON
expand_more
expand_more
format_list_bulleted
Videos
Question
Chapter 6.2, Problem 12E
To determine
To calculation: The system by back substitution.
Expert Solution & Answer
Want to see the full answer?
Check out a sample textbook solution
Students have asked these similar questions
Find the indefinite integral using the substitution x = 5 sin(e). (Use C for the constant of integration.)
1
dx
(25-x²)3/2
Find the indefinite integral using the substitution x = 7 sec(0). (Use C for the constant of integration.)
√ ׳ √x² - 49 dx
Use the Cauchy Riemann equations (polar form version).
Also, describe what happens at the branch cut.
Chapter 6 Solutions
Mathematics with Applications In the Management, Natural and Social Sciences (11th Edition)
Ch. 6.1 - Checkpoint1 Use the substitution method tosolve...Ch. 6.1 - Checkpoint 2
Use the elimination method to solve...Ch. 6.1 - Checkpoint 3
Solve the system of equations .
Draw...Ch. 6.1 - Checkpoint 4
Solve the following system:
Ch. 6.1 - Checkpoint 5
Solve the system
Draw the graph of...Ch. 6.1 - Prob. 6CPCh. 6.1 - Prob. 1ECh. 6.1 - Prob. 2ECh. 6.1 - Use substitution to solve each system. (See...Ch. 6.1 - Use substitution to solve each system. (See...
Ch. 6.1 - Use substitution to solve each system. (See...Ch. 6.1 - Use substitution to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Prob. 12ECh. 6.1 - Prob. 13ECh. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Use elimination to solve each system. (See...Ch. 6.1 - Prob. 16ECh. 6.1 - In Exercises 17 and 18, multiply both sides of...Ch. 6.1 - In Exercises 17 and 18, multiply both sides of...Ch. 6.1 - 19. Business When Neil Simon opened a new play, he...Ch. 6.1 - Prob. 20ECh. 6.1 - 21. Social Science According to U.S. Census Bureau...Ch. 6.1 - 22. Social Science The population y of the given...Ch. 6.1 - Prob. 23ECh. 6.1 - 24. Health The number of deaths y in year x can be...Ch. 6.1 - 25. Business A 200-seat theater charges $8 for...Ch. 6.1 - 26. Business In November 2008, HBO released the...Ch. 6.1 - 27. Physical Science A plane flies 3000 miles from...Ch. 6.1 - 28. Physical Science A plane flying into a...Ch. 6.1 - 29. Finance Shirley Cicero has $16,000 invested in...Ch. 6.1 - 30. Business An apparel shop sells skirts for $45...Ch. 6.1 - Prob. 31ECh. 6.1 - Prob. 32ECh. 6.2 - Checkpoint 1
Use the elimination method to solve...Ch. 6.2 - Prob. 2CPCh. 6.2 - Prob. 3CPCh. 6.2 - Prob. 4CPCh. 6.2 - Prob. 5CPCh. 6.2 - Prob. 6CPCh. 6.2 - Prob. 7CPCh. 6.2 - Checkpoint 8
Solve each system.
(a)
(b)
Ch. 6.2 - Prob. 9CPCh. 6.2 - Prob. 1ECh. 6.2 - Prob. 2ECh. 6.2 - Prob. 3ECh. 6.2 - Prob. 4ECh. 6.2 - Prob. 5ECh. 6.2 - Prob. 6ECh. 6.2 - Obtain an equivalent system by performing the...Ch. 6.2 - Obtain an equivalent system by performing the...Ch. 6.2 - Obtain an equivalent system by performing the...Ch. 6.2 - Prob. 10ECh. 6.2 - Prob. 11ECh. 6.2 - Obtain an equivalent system by performing the...Ch. 6.2 - Prob. 13ECh. 6.2 - Write the augmented matrix of each of the given...Ch. 6.2 - Prob. 15ECh. 6.2 - Prob. 16ECh. 6.2 - Prob. 17ECh. 6.2 - Prob. 18ECh. 6.2 - Prob. 19ECh. 6.2 - Use the indicated row operation to transform each...Ch. 6.2 - In Exercises 21-24, the reduced row echelon form...Ch. 6.2 - In Exercises 21-24, the reduced row echelon form...Ch. 6.2 - In Exercises 21-24, the reduced row echelon form...Ch. 6.2 - In Exercises 21-24, the reduced row echelon form...Ch. 6.2 - In Exercises 25-30, perform row operations on the...Ch. 6.2 - In Exercises 25-30, perform row operations on the...Ch. 6.2 - In Exercises 25-30, perform row operations on the...Ch. 6.2 - Prob. 28ECh. 6.2 - Prob. 29ECh. 6.2 - Prob. 30ECh. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Prob. 36ECh. 6.2 - Prob. 37ECh. 6.2 - Write the augmented matrix of the system and use...Ch. 6.2 - Use the Gauss-Jordan method to solve each of the...Ch. 6.2 - Prob. 40ECh. 6.2 - Prob. 41ECh. 6.2 - Prob. 42ECh. 6.2 - Prob. 43ECh. 6.2 - Prob. 44ECh. 6.2 - Prob. 45ECh. 6.2 - Prob. 46ECh. 6.2 - Prob. 47ECh. 6.2 - Prob. 48ECh. 6.2 - Prob. 49ECh. 6.2 - Solve the system by any method.
50.
Ch. 6.2 - Prob. 51ECh. 6.2 - Prob. 52ECh. 6.2 - Prob. 53ECh. 6.2 - Prob. 54ECh. 6.2 - Prob. 55ECh. 6.2 - Prob. 56ECh. 6.2 - Prob. 57ECh. 6.2 - Prob. 58ECh. 6.2 - Prob. 59ECh. 6.2 - Prob. 60ECh. 6.2 - Prob. 61ECh. 6.2 - Solve the system by any method.
62.
Ch. 6.2 - Prob. 63ECh. 6.2 - Prob. 64ECh. 6.2 - Prob. 65ECh. 6.2 - Prob. 66ECh. 6.2 - Prob. 67ECh. 6.2 - Prob. 68ECh. 6.2 - Prob. 69ECh. 6.2 - Prob. 70ECh. 6.2 - Prob. 71ECh. 6.2 - 72. Explain why a system with more variables than...Ch. 6.3 - Prob. 1CPCh. 6.3 - Prob. 2CPCh. 6.3 - Checkpoint 3
(a) Write the augmented matrix of...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Prob. 5ECh. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - Use systems of equations to work these applied...Ch. 6.3 - A graphing calculator or other technology is...Ch. 6.3 - A graphing calculator or other technology is...Ch. 6.3 - A graphing calculator or other technology is...Ch. 6.3 - A graphing calculator or other technology is...Ch. 6.3 - 25. Social Science The table shows Census Bureau...Ch. 6.3 - 26. Social Science The table shows Census Bureau...Ch. 6.3 - 27. Business At a pottery factory, fuel...Ch. 6.3 - Prob. 28ECh. 6.3 - Prob. 29ECh. 6.3 - Prob. 30ECh. 6.4 - Checkpoint 1
Rewrite matrix M in Example 1 in a...Ch. 6.4 - Prob. 2CPCh. 6.4 - Prob. 3CPCh. 6.4 - Prob. 4CPCh. 6.4 - Prob. 5CPCh. 6.4 - Prob. 6CPCh. 6.4 - Prob. 7CPCh. 6.4 - Prob. 8CPCh. 6.4 - Prob. 9CPCh. 6.4 - Prob. 1ECh. 6.4 - Prob. 2ECh. 6.4 - Prob. 3ECh. 6.4 - Prob. 4ECh. 6.4 - Prob. 5ECh. 6.4 - Prob. 6ECh. 6.4 - Prob. 7ECh. 6.4 - Find the size of each of the given matrices....Ch. 6.4 - Prob. 9ECh. 6.4 - Perform the indicated operations where possible....Ch. 6.4 - Prob. 11ECh. 6.4 - Perform the indicated operations where possible....Ch. 6.4 - Prob. 13ECh. 6.4 - Perform the indicated operations where possible....Ch. 6.4 - Prob. 15ECh. 6.4 - Prob. 16ECh. 6.4 - Prob. 17ECh. 6.4 - Let and . Find each of the following. (See...Ch. 6.4 - Prob. 19ECh. 6.4 - Let and . Find each of the following. (See...Ch. 6.4 - Prob. 21ECh. 6.4 - Let and . Find each of the following. (See...Ch. 6.4 - Prob. 23ECh. 6.4 - Prob. 24ECh. 6.4 - Prob. 25ECh. 6.4 - Prob. 26ECh. 6.4 - Prob. 27ECh. 6.4 - Using matrices
verify that the statements in...Ch. 6.4 - Prob. 29ECh. 6.4 - Prob. 30ECh. 6.4 - Work the following exercises. (See Example...Ch. 6.4 - Work the following exercises. (See Example...Ch. 6.4 - Prob. 33ECh. 6.4 - Prob. 34ECh. 6.4 - Prob. 35ECh. 6.4 - 36. Social Science The following table gives...Ch. 6.4 - 37. Social Science The tables give the death rates...Ch. 6.4 - Prob. 38ECh. 6.5 - Prob. 1CPCh. 6.5 - Prob. 2CPCh. 6.5 - Prob. 3CPCh. 6.5 - Prob. 4CPCh. 6.5 - Prob. 5CPCh. 6.5 - Prob. 6CPCh. 6.5 - Prob. 7CPCh. 6.5 - Prob. 8CPCh. 6.5 - Prob. 9CPCh. 6.5 - Prob. 1ECh. 6.5 - Prob. 2ECh. 6.5 - In Exercises 1-6, the sizes of two matrices A and...Ch. 6.5 - In Exercises 1-6, the sizes of two matrices A and...Ch. 6.5 - Prob. 5ECh. 6.5 - Prob. 6ECh. 6.5 - Prob. 7ECh. 6.5 - Prob. 8ECh. 6.5 - Prob. 9ECh. 6.5 - Prob. 10ECh. 6.5 - Find each of the following matrix products, if...Ch. 6.5 - Prob. 12ECh. 6.5 - Prob. 13ECh. 6.5 - Find each of the following matrix products, if...Ch. 6.5 - Prob. 15ECh. 6.5 - Prob. 16ECh. 6.5 - Prob. 17ECh. 6.5 - Find each of the following matrix products, if...Ch. 6.5 - Prob. 19ECh. 6.5 - Prob. 20ECh. 6.5 - Prob. 21ECh. 6.5 - Prob. 22ECh. 6.5 - Prob. 23ECh. 6.5 - Given matrices
verify that the statements in...Ch. 6.5 - Prob. 25ECh. 6.5 - Prob. 26ECh. 6.5 - Prob. 27ECh. 6.5 - Prob. 28ECh. 6.5 - Prob. 29ECh. 6.5 - Prob. 30ECh. 6.5 - Prob. 31ECh. 6.5 - Determine whether the given matrices are inverses...Ch. 6.5 - Prob. 33ECh. 6.5 - Prob. 34ECh. 6.5 - Prob. 35ECh. 6.5 - Find the inverse, if it exists, for each of the...Ch. 6.5 - Prob. 37ECh. 6.5 - Find the inverse, if it exists, for each of the...Ch. 6.5 - Prob. 39ECh. 6.5 - Prob. 40ECh. 6.5 - Find the inverse, if it exists, for each of the...Ch. 6.5 - Find the inverse, if it exists, for each of the...Ch. 6.5 - Prob. 43ECh. 6.5 - Prob. 44ECh. 6.5 - Prob. 45ECh. 6.5 - Prob. 46ECh. 6.5 - Prob. 47ECh. 6.5 - Prob. 48ECh. 6.5 - Prob. 49ECh. 6.5 - A graphing calculator or other technology is...Ch. 6.5 - Prob. 51ECh. 6.5 - Prob. 52ECh. 6.5 - Prob. 53ECh. 6.5 - Prob. 54ECh. 6.5 - Prob. 55ECh. 6.5 - Prob. 56ECh. 6.6 - Prob. 1CPCh. 6.6 - Prob. 2CPCh. 6.6 - Prob. 3CPCh. 6.6 - Prob. 4CPCh. 6.6 - Prob. 5CPCh. 6.6 - Prob. 6CPCh. 6.6 - Prob. 7CPCh. 6.6 - Checkpoint 8
Use the following matrix to find the ...Ch. 6.6 - Prob. 9CPCh. 6.6 - Prob. 1ECh. 6.6 - Prob. 2ECh. 6.6 - Prob. 3ECh. 6.6 - Prob. 4ECh. 6.6 - Prob. 5ECh. 6.6 - Prob. 6ECh. 6.6 - Prob. 7ECh. 6.6 - Use the inverse of the coefficient matrix to solve...Ch. 6.6 - Prob. 9ECh. 6.6 - Prob. 10ECh. 6.6 - Prob. 11ECh. 6.6 - Use the inverse of the coefficient matrix to solve...Ch. 6.6 - Prob. 13ECh. 6.6 - Prob. 14ECh. 6.6 - Prob. 15ECh. 6.6 - Prob. 16ECh. 6.6 - 17. Business Donovan’s Dandy Furniture makes...Ch. 6.6 - Prob. 18ECh. 6.6 - Prob. 19ECh. 6.6 - Prob. 20ECh. 6.6 - Prob. 21ECh. 6.6 - 22. Health A 100-bed nursing home provides two...Ch. 6.6 - Find the production matrix for the given...Ch. 6.6 - Prob. 24ECh. 6.6 - Prob. 25ECh. 6.6 - Exercises 25 and 26 refer to Example 6.
Example 6...Ch. 6.6 - Prob. 27ECh. 6.6 - Work these problems. (See Examples 3-6.)
28....Ch. 6.6 - Prob. 29ECh. 6.6 - Prob. 30ECh. 6.6 - Prob. 31ECh. 6.6 - Prob. 32ECh. 6.6 - Prob. 33ECh. 6.6 - Prob. 34ECh. 6.6 - Prob. 35ECh. 6.6 - Prob. 36ECh. 6.6 - Prob. 37ECh. 6.6 - Prob. 38ECh. 6.6 - Prob. 39ECh. 6.6 - Prob. 40ECh. 6.6 - Prob. 41ECh. 6.6 - Prob. 42ECh. 6.6 - Prob. 43ECh. 6.6 - 44. Business The figure shows four southern cities...Ch. 6.6 - Prob. 45ECh. 6 - Prob. 1CECh. 6 - 2. It was shown previously that there are four...Ch. 6 - 3. Which trips in the Stampede Air network take...Ch. 6 - Prob. 4CECh. 6 - Prob. 5CECh. 6 - Prob. 6CECh. 6 - Prob. 1RECh. 6 - Solve each of the following systems.
2.
Ch. 6 - Solve each of the following systems.
3.
Ch. 6 - Solve each of the following systems.
4.
Ch. 6 - 5. Business Abigail Henderson plans to buy shares...Ch. 6 - Prob. 6RECh. 6 - Prob. 7RECh. 6 - Prob. 8RECh. 6 - Prob. 9RECh. 6 - Prob. 10RECh. 6 - Prob. 11RECh. 6 - Prob. 12RECh. 6 - Prob. 13RECh. 6 - Prob. 14RECh. 6 - Prob. 15RECh. 6 - Prob. 16RECh. 6 - Prob. 17RECh. 6 - Prob. 18RECh. 6 - Prob. 19RECh. 6 - Prob. 20RECh. 6 - Prob. 21RECh. 6 - Prob. 22RECh. 6 - Prob. 23RECh. 6 - Prob. 24RECh. 6 - Prob. 25RECh. 6 - Prob. 26RECh. 6 - Prob. 27RECh. 6 - Prob. 28RECh. 6 - Prob. 29RECh. 6 - Prob. 30RECh. 6 - Prob. 31RECh. 6 - Prob. 32RECh. 6 - Prob. 33RECh. 6 - Prob. 34RECh. 6 - Prob. 35RECh. 6 - Prob. 36RECh. 6 - Prob. 37RECh. 6 - Prob. 38RECh. 6 - Prob. 39RECh. 6 - Prob. 40RECh. 6 - Prob. 41RECh. 6 - Prob. 42RECh. 6 - Prob. 43RECh. 6 - Prob. 44RECh. 6 - Prob. 45RECh. 6 - Prob. 46RECh. 6 - Prob. 47RECh. 6 - Prob. 48RECh. 6 - Prob. 49RECh. 6 - Prob. 50RECh. 6 - Prob. 51RECh. 6 - Prob. 52RECh. 6 - Prob. 53RECh. 6 - Prob. 54RECh. 6 - Prob. 55RECh. 6 - Prob. 56RECh. 6 - Prob. 57RECh. 6 - Prob. 58RECh. 6 - Prob. 59RECh. 6 - Prob. 60RECh. 6 - Prob. 61RECh. 6 - Prob. 62RECh. 6 - Prob. 63RECh. 6 - Prob. 64RECh. 6 - Prob. 65RECh. 6 - Prob. 66RECh. 6 - Prob. 67RECh. 6 - Prob. 68RECh. 6 - Prob. 69RECh. 6 - Prob. 70RECh. 6 - Prob. 71RECh. 6 - Prob. 72RECh. 6 - Prob. 73RECh. 6 - Prob. 74RECh. 6 - Prob. 75RECh. 6 - Prob. 76RECh. 6 - Prob. 77RECh. 6 - Prob. 78RECh. 6 - Prob. 79RECh. 6 - Prob. 80RECh. 6 - Prob. 81RECh. 6 - Prob. 82RECh. 6 - Prob. 83RECh. 6 - Prob. 84RECh. 6 - Prob. 85RECh. 6 - Solve each of the following problems by any...Ch. 6 - Prob. 87RECh. 6 - Prob. 88RECh. 6 - Prob. 89RECh. 6 - Use technology to do Exercises 89-91.
90. Business...Ch. 6 - Prob. 91RECh. 6 - Prob. 92RECh. 6 - Prob. 93RECh. 6 - Prob. 94RE
Knowledge Booster
Learn more about
Need a deep-dive on the concept behind this application? Look no further. Learn more about this topic, subject and related others by exploring similar questions and additional content below.Similar questions
- b. i. Show that the following matrix is orthogonal. A = ドードー ii Find the inverse of matrix A. Show all working in an organized/orderly manner. 2 3 -619 A = 42 3 1 5 B-1127) a. Given D = , decode the following message: 32, 24, 42, 28, 24, 40, 50, 60, 132, 96, 12, 24arrow_forward2 Graph of h 6. The graph of the function h is given in the xy-plane. Which of the following statements is correct? , the graph of h is increasing at an increasing rate. (A) For (B) For (C) For 苏|4 K|4 π π , the graph of h is increasing at a decreasing rate. 2 0 and b>1 (B) a>0 and 01 (D) a<0 and 0arrow_forwardQUESTION 4 Peter says that the following expressions can be simplified into one trigonometric ratio without the use of a calculator. Prove that Peter is correct by simplifying the following expressions into one trigonometric ratio: 4.1 sin 43° + sin 17º (5)arrow_forward3. Consider the sequences of functions fn: [-T, π] → R, sin(n²x) n(2) n (i) Find a function f : [-T, π] R such that fnf pointwise as n∞. Further, show that f uniformly on [-T,π] as n→ ∞. [20 Marks] (ii) Does the sequence of derivatives f(x) has a pointwise limit on [-7,π]? Justify your answer. [10 Marks]arrow_forwardAmong a student group 54% use Google Chrome, 20% Internet Explorer, 10% Firefox, 5% Mozilla, and the rest use Safari. What is the probability that you need to pick 7 students to find 2 students using Google Chrome? Report answer to 3 decimals.arrow_forwardQuestion 3 a. Using Laplace theorem, find the determinant of the following matrix. 3 5 2 4 1 3 7 6 A= 2 48 3 569 7arrow_forwardSamples of rejuvenated mitochondria are mutated (defective) with a probability 0.13. Find the probability that at most one sample is mutated in 10 samples. Report answer to 3 decimal places.arrow_forwardGood Day, Please assist with the following. Regards,arrow_forwardChoose all of the statements that are true: 16 is even -16 is even 401 is even √2 is even π is even 2π is even If n is an integer, then n(n + 1) is always even.arrow_forwardIs the number "-4" even, odd, or neither? Use the definition of even/odd to explain why your answer makes sense.arrow_forwardCustomers experiencing technical difficulty with their Internet cable service may call an 800 number for technical support. It takes the technician between 30 seconds and 11 minutes to resolve the problem. The distribution of this support time follows the uniform distribution. Required: a. What are the values for a and b in minutes? Note: Do not round your intermediate calculations. Round your answers to 1 decimal place. b-1. What is the mean time to resolve the problem? b-2. What is the standard deviation of the time? c. What percent of the problems take more than 5 minutes to resolve? d. Suppose we wish to find the middle 50% of the problem-solving times. What are the end points of these two times?arrow_forwardExercise 6-6 (Algo) (LO6-3) The director of admissions at Kinzua University in Nova Scotia estimated the distribution of student admissions for the fall semester on the basis of past experience. Admissions Probability 1,100 0.5 1,400 0.4 1,300 0.1 Click here for the Excel Data File Required: What is the expected number of admissions for the fall semester? Compute the variance and the standard deviation of the number of admissions. Note: Round your standard deviation to 2 decimal places.arrow_forwardarrow_back_iosSEE MORE QUESTIONSarrow_forward_ios
Recommended textbooks for you
Discrete Mathematics and Its Applications ( 8th I...MathISBN:9781259676512Author:Kenneth H RosenPublisher:McGraw-Hill Education
Mathematics for Elementary Teachers with Activiti...MathISBN:9780134392790Author:Beckmann, SybillaPublisher:PEARSON
Thinking Mathematically (7th Edition)MathISBN:9780134683713Author:Robert F. BlitzerPublisher:PEARSON
Discrete Mathematics With ApplicationsMathISBN:9781337694193Author:EPP, Susanna S.Publisher:Cengage Learning,
Pathways To Math Literacy (looseleaf)MathISBN:9781259985607Author:David Sobecki Professor, Brian A. MercerPublisher:McGraw-Hill Education
Discrete Mathematics and Its Applications ( 8th I...
Math
ISBN:9781259676512
Author:Kenneth H Rosen
Publisher:McGraw-Hill Education
Mathematics for Elementary Teachers with Activiti...
Math
ISBN:9780134392790
Author:Beckmann, Sybilla
Publisher:PEARSON
Thinking Mathematically (7th Edition)
Math
ISBN:9780134683713
Author:Robert F. Blitzer
Publisher:PEARSON
Discrete Mathematics With Applications
Math
ISBN:9781337694193
Author:EPP, Susanna S.
Publisher:Cengage Learning,
Pathways To Math Literacy (looseleaf)
Math
ISBN:9781259985607
Author:David Sobecki Professor, Brian A. Mercer
Publisher:McGraw-Hill Education
Matrix Factorization - Numberphile; Author: Numberphile;https://www.youtube.com/watch?v=wTUSz-HSaBg;License: Standard YouTube License, CC-BY