已知tanα=-1/3,则1/2sinαcosα+cos2α=10/3?
问题描述:
已知tanα=-1/3,则1/2sinαcosα+cos2α=10/3?
答
1/2sinαcosα+cos2α
=1/4sin2α+cos2α
=1/4*2tanα/[1+(tanα)^2]+[1-(tanα)^2]/[1+(tanα)^2]
=1/4*(-3/5)+4/5
=13/20