Question

find intervals sin3x between 0- pi/2

Answer 1

I'd suggest you do this problem in at least 2 different ways to ascertain that you're getting the correct answers.

First, you might want to graph y=sin 3x on [0, pi/2]. Before you try that, please explain what you mean by "find intervals." What kind of intervals are you looking for?

Answer 2

For example, you might be asking, "Identify the intervals on [0, pi/2] for which the graph of y=sin 3x is positive." Remove the ambiguity about what you're looking for.