已知sinα=4/5,则cos2α=

问题描述:

已知sinα=4/5,则cos2α=

cos2α=1-2(sinα)^2=1-32/25=-7/25

已知sinα=4/5
则cos2α=1-2sin²α=1-2*(4/5)²=-7/25

cos2α=1-2sin²a=1-2×16/25=-7/25

-7/25