若tanα=1/3则sin^2α-sinαcosα-cos^2α=

问题描述:

若tanα=1/3则sin^2α-sinαcosα-cos^2α=

sin^2α-sinαcosα-cos^2α
=(sin^2α-sinαcosα-cos^2α)/(sin²a+cos²a)
=(tan²a-tana-1)/(tan²a+1) 分子分母同时除以cos²a
=(1/9-1/3-1)/(1/9+1)
=-11/10