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MTH 102 MTH 102 Past Questions Objective Question

Question

Evaluate ∫ (e2x + e-2x)⁄(e2x - e-2x) dx.
Options
A <sup>1</sup>&frasl;<sub>4</sub> ln|e<sup>2x</sup> - e<sup>-2x</sup>| + C
B <sup>1</sup>&frasl;<sub>2</sub> ln|e<sup>2x</sup> + e<sup>-2x</sup>| + C
C <sup>1</sup>&frasl;<sub>2</sub> ln|e<sup>2x</sup> - e<sup>-2x</sup>| + C
Correct Answer
D <sup>1</sup>&frasl;<sub>4</sub> ln|e<sup>2x</sup> + e<sup>-2x</sup>| + C
Correct Answer

Option C is the correct answer.

Detailed Explanation

This integral is of the form ∫ f'(x)⁄f(x) dx = ln|f(x)| + C.Let u = e2x - e-2x (the denominator).Then, find du/dx:du/dx = d/dx(e2x) - d/dx(e-2x)= (2e2x) - (-2e-2x)= 2e2x + 2e-2x = 2(e2x + e-2x).So, du = 2(e2x + e-2x) dx.This means (1⁄2) du = (e2x + e-2x) dx (the numerator).Substitute u and (1⁄2)du into the integral:∫ 1⁄u (1⁄2) du = 1⁄2 ∫ 1⁄u du= 1⁄2 ln|u| + CSubstitute back u = e2x - e-2x:= 1⁄2 ln|e2x - e-2x| + C.This matches option C.

Hint

Look for a function and its derivative. The derivative of the denominator is proportional to the numerator. Use u-substitution.

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