## Thomas' Calculus 13th Edition

$\dfrac{3}{5} \sin 5\theta +C$
Here, $\int (3 \cos 5\theta) d\theta=\dfrac{3}{5} \sin 5\theta +C$ Also, $\dfrac{d}{d \theta}(\dfrac{3}{5} \sin 5\theta +C )=3 \cos 5\theta$ Thus, the derivative of the integral is integrand. So, the answer is correct.