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MTH 102 MTH 102 Past Questions Objective Question

Question

Evaluate ∫ (e2x + e-2x) / (e2x - e-2x) dx
Options
A (1/4) ln|<i>e</i><sup>2<i>x</i></sup> - <i>e</i><sup>-2<i>x</i></sup>| + C
B (1/2) ln|<i>e</i><sup>2<i>x</i></sup> + <i>e</i><sup>-2<i>x</i></sup>| + C
C (1/2) ln|<i>e</i><sup>2<i>x</i></sup> - <i>e</i><sup>-2<i>x</i></sup>| + C
Correct Answer
D (1/4) ln|<i>e</i><sup>2<i>x</i></sup> + <i>e</i><sup>-2<i>x</i></sup>| + C
Correct Answer

Option C is the correct answer.

Detailed Explanation

This integral can be solved using a u-substitution.Let u = e2x - e-2x.Now, find du/dx:du/dx = d/dx(e2x) - d/dx(e-2x)Using the chain rule, d/dx(eax) = a eax:du/dx = (2e2x) - (-2e-2x)du/dx = 2e2x + 2e-2xdu/dx = 2(e2x + e-2x)So, du = 2(e2x + e-2x) dx.This means (e2x + e-2x) dx = (1/2)du.Substitute u and du into the integral:∫ (1/u) * (1/2) du = (1/2) ∫ (1/u) duNow, integrate with respect to u:= (1/2) ln|u| + CSubstitute u = e2x - e-2x back into the expression:= (1/2) ln|e2x - e-2x| + CThis matches option C.

Hint

Consider a u-substitution where u is the denominator of the integrand. Check if the derivative of the denominator matches the numerator (or a multiple of it).

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