已知:tanα=3,则sin平方α-cos平方α=

问题描述:

已知:tanα=3,则sin平方α-cos平方α=

sin²α-cos²α
=(sin²α-cos²α)/1
=(sin²α-cos²α)/(sin²α+cos²α)
=(tan²α-1)/(tan²α+1)
=(9-1)/(9+1)
=4/5