Find the (1, 1) entry of the matrix product XY using the matrices below: a X = b and Y = | c 1 -1 d and where a = 5, b = 5, c = 7, and d = 1

Algebra and Trigonometry (6th Edition)
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ChapterP: Prerequisites: Fundamental Concepts Of Algebra
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Problem 1MCCP: In Exercises 1-25, simplify the given expression or perform the indicated operation (and simplify,...
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**Matrix Multiplication Problem**

To find the entry (1, 1) of the matrix product \( XY \), we will use the matrices below:

\[
X = \begin{pmatrix}
a \\
b \\
1 \\
\end{pmatrix}
\quad \text{and} \quad
Y = \begin{pmatrix}
c & -1 & d \\
\end{pmatrix}
\]

We are given the values: 
\[ a = -5, \; b = 5, \; c = 7, \; \text{and} \; d = 1 \]

**Step-by-Step Solution:**

1. First, substitute the given values into the matrices \( X \) and \( Y \):

\[
X = \begin{pmatrix}
-5 \\
5 \\
1 \\
\end{pmatrix}
\quad \text{and} \quad
Y = \begin{pmatrix}
7 & -1 & 1 \\
\end{pmatrix}
\]

2. Perform the matrix multiplication \( XY \) to find the (1, 1) entry. The (1, 1) entry of the product \( XY \) is obtained by summing the products of corresponding entries from the first row of \( X \) and the first column of \( Y \):

\[
XY = (-5 \times 7) + (5 \times -1) + (1 \times 1)
\]

3. Calculate the products and their sum:

\[
XY = (-35) + (-5) + 1 = -35 - 5 + 1 = -39
\]

Therefore, the (1, 1) entry of the matrix product \( XY \) is \( -39 \).

**Final Answer:**

Enter your answer as a whole number. For example: 23 or 135 or 8.

\[
\boxed{-39}
\]
Transcribed Image Text:**Matrix Multiplication Problem** To find the entry (1, 1) of the matrix product \( XY \), we will use the matrices below: \[ X = \begin{pmatrix} a \\ b \\ 1 \\ \end{pmatrix} \quad \text{and} \quad Y = \begin{pmatrix} c & -1 & d \\ \end{pmatrix} \] We are given the values: \[ a = -5, \; b = 5, \; c = 7, \; \text{and} \; d = 1 \] **Step-by-Step Solution:** 1. First, substitute the given values into the matrices \( X \) and \( Y \): \[ X = \begin{pmatrix} -5 \\ 5 \\ 1 \\ \end{pmatrix} \quad \text{and} \quad Y = \begin{pmatrix} 7 & -1 & 1 \\ \end{pmatrix} \] 2. Perform the matrix multiplication \( XY \) to find the (1, 1) entry. The (1, 1) entry of the product \( XY \) is obtained by summing the products of corresponding entries from the first row of \( X \) and the first column of \( Y \): \[ XY = (-5 \times 7) + (5 \times -1) + (1 \times 1) \] 3. Calculate the products and their sum: \[ XY = (-35) + (-5) + 1 = -35 - 5 + 1 = -39 \] Therefore, the (1, 1) entry of the matrix product \( XY \) is \( -39 \). **Final Answer:** Enter your answer as a whole number. For example: 23 or 135 or 8. \[ \boxed{-39} \]
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