Hi. This calculus problem has given me fits for the last few days:

Find the extrema of y=sinx + cosx on the interval [0,2pi]

I tried going at it regularly by taking the first derivative (y'=cosx - sinx) then setting it equal to 0. I just can't solve for "x" past that point. I think logically I should do (cosx = sinx), but then I can't remember that ancient trig. stuff to solve for "x". I could be going at it all wrong, though.

Does anyone have any suggestions?