1. The problem statement, all variables and given/known data let g be a function mapping x to xcosx-sinx. use the mean value theorem to prove that g(x) < 0 for x in (0,pi] 2. Relevant equations well the function is both continuous and differentiable on the interval so that's a start... 3. The attempt at a solution basically i thought i'd separate the interval into smaller sections coinciding with the roots of xcosx and sinx, ie: i ticked off the interval [pi/2,pi] as xcosx is negative and sinx is still positive so g(x) <0; currently considering xcosx for x in (0,1) and trying to find a turning point but i'm not seeing anywhere i can actually apply the MVT at the moment... halp!