Hey, I have a test coming up this week and I not sure how to do these two questions.

If y=3x.cosx , show that the truning point of curve occurs only when x=cos x/sin x

I got as far as dy/dx = 3(x-3sin3x+cos3x)=0 but then i dont know what to do after that. I am not sure if thats right

If y=2x^2.cos3x, show that the turning point of curve occurs at point where x=0 and also whenever x= 2cos3x/3sin3x

I got as fas as dy/dx= 2x(x-3sin3x+2cos3x)=0 then i am not sure what to do next.

Thanks.

set the derivative = 0