trigonometry problem

[Constantinos]

This is not homework question, just curious about it though. This problem is supposed to be done without a computing device and was in an exam at a university course. I don't think it can be done.

1. The problem statement, all variables and given/known data
I want to find the maximum of this function:

Y = sin(x) + sin(2x)

2. Relevant equations



3. The attempt at a solution

Attempted sin(2x) = 2sinx*cosx, tried to draw it, tried to go euler's formula, no luck whatsoever (of course I take the derivative!)

Mathematica gives me this:

FindMaximum[Sin[x] + Sin[2*x], {x, 0}]

Out[1]= {1.76017, {x -> 0.935929}}

Any ideas? It really seems simple, but I just can't figure it out...

Thanks!

[rock.freak667]

Why don't you just solve dy/dx = 0 and then sub cos(2x) as 2cos2-1 ?

You should get a quadratic in cosx to solve.

[Constantinos]

Why don't you just solve dy/dx = 0 and then sub cos(2x) as 2cos2-1 ?

You should get a quadratic in cosx to solve.

Lol where is my mind! Thanks :P