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MTH 102 MTH 102 Past Questions Objective Question

Question

Simplify ∫ ex sinx dx
Options
A <i>e<sup>x</sup>/4 (cos x - sin<sup>2</sup>x) + C</i>
B <i>e<sup>x</sup>/3 (cos<sup>2</sup>x + sin x) + C</i>
C <i>e<sup>x</sup>/2 (sin x - cos x) + C</i>
Correct Answer
D <i>e<sup>x</sup> (cos x - sin x) + C</i>
Correct Answer

Option C is the correct answer.

Detailed Explanation

This integral requires integration by parts, which is given by ∫ u dv = uv - ∫ v du.Let ∫ I = ex sinx dx.Choose u = sin x and dv = ex dx.Then du = cos x dx and v = ex.Substitute into the formula:I = ex sin x - ∫ ex cos x dx.Now, we need to evaluate ∫ ex cos x dx. We apply integration by parts again.Let u' = cos x and dv' = ex dx.Then du' = -sin x dx and v' = ex.So, ∫ ex cos x dx = ex cos x - ∫ ex (-sin x) dx = ex cos x + ∫ ex sin x dx.Substitute this back into the expression for I:I = ex sin x - (ex cos x + ∫ ex sin x dx)I = ex sin x - ex cos x - I.Add I to both sides:2I = ex sin x - ex cos x.Finally, solve for I:I = (ex sin x - ex cos x)/2 + CI = ex/2 (sin x - cos x) + C. This matches option C.

Hint

Use integration by parts (∫ u dv = uv - ∫ v du) twice. You will find the original integral reappears on the right side, allowing you to solve for it algebraically.

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