8.3.43) Queetion: Tind the volumeof the solid. The region bounded ou f-e-* X=In2, and the coordinate axes brevolved about trev |(tan 4a)(sec 4x – 1) da = | (tan 4r) sec² 4x da – tan 4r dr = tan 4r dr axis.

Advanced Engineering Mathematics
10th Edition
ISBN:9780470458365
Author:Erwin Kreyszig
Publisher:Erwin Kreyszig
Chapter2: Second-order Linear Odes
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The question is circled in bright yellow. My question is, where did the tan^3 4xdx come from?

### Section 8.3.43

**Question:** Find the volume of the solid. The region bounded by \( f(x) = e^{-x} \), \( x = \ln 2 \), and the coordinate axes is revolved about the y-axis.

#### Solution:

To solve the given problem, we first address the integration involved:

\[
\int \tan^3 4x \, dx = \int (\tan 4x)(\sec^2 4x - 1) \, dx = \int (\tan 4x) \sec^2 4x \, dx - \int \tan 4x \, dx
\]

This can be rewritten as:

\[
= \int (\tan 4x) \sec^2 4x \, dx + \frac{\ln |\cos 4x|}{4} + C
\]

Now, let's substitute:

Let \( u = \tan 4x \) so that \( du = 4 \sec^2 4x \, dx \). Substituting gives:

\[
\frac{1}{4} \int u \, du + \frac{\ln |\cos 4x|}{4} + C = \frac{u^2}{8} + \frac{\ln |\cos 4x|}{4} + C
\]

This can be further simplified to:

\[
= \frac{\tan^2 4x}{8} + \frac{\ln |\cos 4x|}{4} + C
\]

This step-by-step solution shows the integration process used to find the area under the curve, which is necessary to compute the volume of the solid revolved about the y-axis.
Transcribed Image Text:### Section 8.3.43 **Question:** Find the volume of the solid. The region bounded by \( f(x) = e^{-x} \), \( x = \ln 2 \), and the coordinate axes is revolved about the y-axis. #### Solution: To solve the given problem, we first address the integration involved: \[ \int \tan^3 4x \, dx = \int (\tan 4x)(\sec^2 4x - 1) \, dx = \int (\tan 4x) \sec^2 4x \, dx - \int \tan 4x \, dx \] This can be rewritten as: \[ = \int (\tan 4x) \sec^2 4x \, dx + \frac{\ln |\cos 4x|}{4} + C \] Now, let's substitute: Let \( u = \tan 4x \) so that \( du = 4 \sec^2 4x \, dx \). Substituting gives: \[ \frac{1}{4} \int u \, du + \frac{\ln |\cos 4x|}{4} + C = \frac{u^2}{8} + \frac{\ln |\cos 4x|}{4} + C \] This can be further simplified to: \[ = \frac{\tan^2 4x}{8} + \frac{\ln |\cos 4x|}{4} + C \] This step-by-step solution shows the integration process used to find the area under the curve, which is necessary to compute the volume of the solid revolved about the y-axis.
Expert Solution
Step 1

No need for this term for evaluating the volume of the revolved solid. 

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