Answer
The graphs appear to coincide.
Work Step by Step
$$\sin 3x + \sin x = 2 \sin \frac{3x+x}{2}\cos \frac{3x-x}{2}=2\sin 2x \cos x$$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.