30. If f(t) = sec t, find f"(π/4)

Calculus: Early Transcendentals
8th Edition
ISBN:9781285741550
Author:James Stewart
Publisher:James Stewart
Chapter1: Functions And Models
Section: Chapter Questions
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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**Problem 30:**

Given the function \( f(t) = \sec t \), find the second derivative \( f''(\pi/4) \).

**Solution Approach:**

1. **Find the First Derivative**:  
   The derivative of \( \sec t \) with respect to \( t \) is \( f'(t) = \sec t \tan t \).

2. **Find the Second Derivative**:  
   Differentiate \( f'(t) = \sec t \tan t \) with respect to \( t \) to obtain \( f''(t) \).

3. **Evaluate at \( t = \pi/4 \)**:  
   Substitute \( t = \pi/4 \) into \( f''(t) \) to find \( f''(\pi/4) \).

**Calculation Steps**:

- First, find the derivative of \( \sec t \):
  \[
  f'(t) = \sec t \tan t
  \]

- Then, differentiate \( f'(t) \) to find \( f''(t) \):
  \[
  f''(t) = \frac{d}{dt}(\sec t \tan t)
  \]

- Apply the product rule: if \( u = \sec t \) and \( v = \tan t \), then:
  \[
  f''(t) = u'v + uv' = (\sec t \tan t)\tan t + (\sec t)(\sec^2 t)
  \]

  Simplifying further:
  \[
  f''(t) = \sec t \tan^2 t + \sec^3 t
  \]

- Evaluate at \( t = \pi/4 \):
  - \(\sec(\pi/4) = \sqrt{2}\)
  - \(\tan(\pi/4) = 1\)

  Substitute into \( f''(t) \):
  \[
  f''(\pi/4) = \sqrt{2} \cdot 1^2 + (\sqrt{2})^3 
  \]
  \[
  f''(\pi/4) = \sqrt{2} + 2\sqrt{2} = 3\sqrt{2}
  \]

Thus, the second derivative of the function at \( t = \pi/
Transcribed Image Text:**Problem 30:** Given the function \( f(t) = \sec t \), find the second derivative \( f''(\pi/4) \). **Solution Approach:** 1. **Find the First Derivative**: The derivative of \( \sec t \) with respect to \( t \) is \( f'(t) = \sec t \tan t \). 2. **Find the Second Derivative**: Differentiate \( f'(t) = \sec t \tan t \) with respect to \( t \) to obtain \( f''(t) \). 3. **Evaluate at \( t = \pi/4 \)**: Substitute \( t = \pi/4 \) into \( f''(t) \) to find \( f''(\pi/4) \). **Calculation Steps**: - First, find the derivative of \( \sec t \): \[ f'(t) = \sec t \tan t \] - Then, differentiate \( f'(t) \) to find \( f''(t) \): \[ f''(t) = \frac{d}{dt}(\sec t \tan t) \] - Apply the product rule: if \( u = \sec t \) and \( v = \tan t \), then: \[ f''(t) = u'v + uv' = (\sec t \tan t)\tan t + (\sec t)(\sec^2 t) \] Simplifying further: \[ f''(t) = \sec t \tan^2 t + \sec^3 t \] - Evaluate at \( t = \pi/4 \): - \(\sec(\pi/4) = \sqrt{2}\) - \(\tan(\pi/4) = 1\) Substitute into \( f''(t) \): \[ f''(\pi/4) = \sqrt{2} \cdot 1^2 + (\sqrt{2})^3 \] \[ f''(\pi/4) = \sqrt{2} + 2\sqrt{2} = 3\sqrt{2} \] Thus, the second derivative of the function at \( t = \pi/
Expert Solution
Step 1

Topic- Double derivative of a function.

we are given

f(t)=sec t

and we know that

ddtsec t=sec(t) tan(t)ddttan t=sec2(t)ddtu·v=uddtv+vddtu

steps

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