Sin2(x) +cos(x)=1 from the relation: (sin2(x) +cos2(x) =1 ) so , sin2(x)=1-cos2(x) by subs. in the main eqn. 1-cos2(x) + cos(x) =1 by simplify the eqn. cos(x) -cos2(x)=0 take cos(x) as a common factor cos(x)* (1-cos(x))=0 then cos(x)=0 && cos(x)=1 cos(x)=0 if x= pi/2 & cos(x) = 1 if x = 0 , 2*pi so the solution is x= {0,pi/2 , 2*pi}