解:
(1)
y=sinx^2+sin2x+3cosx^2=-1/2(-2sin^2x+1-1)+sin2x+3/2(2cos^2x-1+1)
=-1/2cos2x+1/2+sin2x+3/2cos2x+3/2
=cos2x+sin2x+2
=根号2sin(2x+π/4) +2
所以最小值为2-根号2
此时x=5π/8+kπ
(2)
y=根号2sin(2x+π/4) +2
所以当
-π/2+2kπ