Question

已知tanα＝2求sin²α–cos²α的值

Answer 1

tanα＝2求sin²α–cos²α
tanα＝2
sinα/cosα=2
sin²α/cos²α=4
sin²α=4cos²α
sin²α+cos²α=1
5cos²α=1
cos²α=0.2
sin²α=0.8
sin²α–cos²α=0.8-0.2=0.6

Answer 2

tanα=2
sinα = 2/√5 or -2/√5
cosα = 1/√5 or -1/√5

sin²α–cos²α
=4/5- 1/5
=3/5