y=(sinx)^2+sin2x+3(cosx)^2利用2倍角公式 =(1-cos2x)/2+sin2x+3(1+cos2x)/2 =cos2x+sin2x+2 =√2sin(2x+π/4)+2 1.取最小值时 sin(2x+π/4)=-1 2x+π/4=2kπ+3π/2 x=kπ+5π/8 k是整数 {x|x=kπ+5π/8,k是整数} 2....