y
=2cosxsinx+2cosx*cosx
=sin2x+(2cosx*cosx-1)+1
=sin2x+cos2x+1
=根号2*sin(2x+45)+1
=>递增区间为
-pi/2+2pi*N<2x+45=>-3pi/4+2pi*N<2x=>-3pi/8+pi*N(N为整数)