Let f be the function defin 2x f(x)3= D{ 1 a) For what values of k b) Using the value k fo x= 2. Use the defin c) Let k =4. Determin

Calculus: Early Transcendentals
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Chapter1: Functions And Models
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Problem 1RCC: (a) What is a function? What are its domain and range? (b) What is the graph of a function? (c) How...
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Let \( f \) be the function defined as follows:

\[
f(x) = 
\begin{cases} 
2x + 1, & \text{for } x \leq 2 \\
\frac{1}{2}x^2 + k, & \text{for } x > 2 
\end{cases}
\]

a) For what values of \( k \) will \( f \) be continuous at \( x = 2 \)? Justify your answer.

b) Using the value of \( k \) found in part a), determine whether \( f \) is differentiable at \( x = 2 \). Use the definition of the derivative to justify your answer.

c) Let \( k = 4 \). Determine whether \( f \) is differentiable at \( x = 2 \). Justify your answer.
Transcribed Image Text:Let \( f \) be the function defined as follows: \[ f(x) = \begin{cases} 2x + 1, & \text{for } x \leq 2 \\ \frac{1}{2}x^2 + k, & \text{for } x > 2 \end{cases} \] a) For what values of \( k \) will \( f \) be continuous at \( x = 2 \)? Justify your answer. b) Using the value of \( k \) found in part a), determine whether \( f \) is differentiable at \( x = 2 \). Use the definition of the derivative to justify your answer. c) Let \( k = 4 \). Determine whether \( f \) is differentiable at \( x = 2 \). Justify your answer.
Expert Solution
Step 1

Given that,

f(x)=2x+1,       for x212x2+k,    for x > 2

(a)

If the function is continuous at x = 2, one-sided limits are equal.

That is,

limx2-f(x)=limx2+f(x)limx22x+1=limx212x2+k22+1=1222+k5=2+k5-2=kk=3

The function is continuous at x = 2 for k = 3.

Step 2

(b)

A function is differentiable at x= c if and only if the left and right derivatives at c both exist and are equal.

Substitute k = 3 in the given function.

f(x)=2x+1,       for x212x2+3,    for x > 2

To find left-sided derivative at x = 2, find derivative of 2x + 1 at x = 2. 

Definition of derivative of f(x) at point x = a is

f'(a)=limh0fa+h-fah

f'(2)=limh0f2+h-f2h=limh022+h+1-[22+1]h=limh04+2h+1-[5]h=limh05+2h-5h=limh02hhf'(2-)=2

The left-sided derivative at x = 2 is 2. 

To find left-sided derivative at x = 2, find derivative of 12x2+3 at x = 2. 

f'(2+)=limh0f2+h-f2h=limh0122+h2+3-[1222+3]h=limh0124+4h+h2+3-[5]h=limh02+2h+h22+3-[5]h=limh02h+h22h=limh02+h2=2+02f'(2+)=2

The right-sided derivative at x = 2 is 2.

Here the left and right derivatives at x= 2 both exist and are equal.

The function is differentiable at x = 2. 

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