饭桌上的战争
幼苗
共回答了24个问题采纳率:91.7% 举报
y = sin(π/2+x)*(sinx+cosx)
= cosx *(sinx+cosx)
= sinxcosx+cos²x
= 1/2sin2x + 1/2(cos2x-1)
= 1/2(sin2x+cos2x) - 1/2
= √2/2(sin2xcosπ/4+cos2xsinπ/4) - 1/2
= √2/2sin(2x+π/4) - 1/2
sin(2x+π/4)最小值-1
∴ymin = -√2/2-1/2 = -(√2+1)/2
1年前
4