Integration by parts twiceHardQuestion 330011
Question
∫eˣ sin x dx equals:
- Aeˣ(sin x − cos x)/2 + CCorrect
- Beˣ sin x + C
- Ceˣ cos x + C
- D−eˣ cos x + C
Correct answer
eˣ(sin x − cos x)/2 + C
Explanation
Let I = ∫eˣ sin x dx. By parts twice: I = eˣ sin x − ∫eˣ cos x dx = eˣ sin x − (eˣ cos x + ∫eˣ sin x dx) = eˣ(sin x − cos x) − I. 2I = eˣ(sin x − cos x) + C → I = eˣ(sin x − cos x)/2 + C.