若tanα=1/2,则cos²α-sin²α的值为

问题描述:

若tanα=1/2,则cos²α-sin²α的值为

cos²α-sin²α
=(cos²α-sin²α)/(cos²α+sin²α)
=(1-tan²α)/(1+tan²α)
=(1-1/4)/(1+1/4)
=3/5