4cos^2 x - cosx-3 =0
0 to 2pi
SORRY TYPED THE QUESTION WRONG PLESSE HELP
let cosx = t, then your equation becomes
4t^2 - t - 3 = 0
(4t + 3)(t - 1) = 0
t= -3/4 or t = 1
cosx = -3/4 or cosx = 1
now follow the steps I used for your previous post when you were Sara
http://www.jiskha.com/display.cgi?id=1490924093