#1**+1 **

I will assume that you mean

f(x) = sin3xcosx/(tan2x+1) this has no global maximum (ref: Wolframalpha)

so maybe you mean

f(x) = (sin3xcosx/tan2x)+1 (yes I know this is how it should be interpreted bum a loy of people make mistakes here)

I spent ages working on the first interpretation, I haven't got the energy to look at this second one at present but Wolfram Alpha says the maximum is 2.5

Melody Oct 16, 2018