tan=1/3,则2sin²α-(3sinαcosα/2)+5cos²α=?
问题描述：
tan=1/3,则2sin²α-(3sinαcosα/2)+5cos²α=?
答
sin2α = 2tana /(1+tan²α) = 0.6
cos2α = (1-tan²α)/(1+tan²α) = 0.8
2sin²α-(3sinαcosα/2)+5cos²α
= 1-cos2α + 3sin2α/4 + 5(1+cos2α)/2
= 4.25