Question

怎么做呢？谢谢！

Answer 1

Answer 2

sin(π/2-α)＝sin(π/2)cosα-cos(π/2)sinα=1*cosα-0*sinα=cosα

追问

不用公式怎么做

追答

sin(π/2-α)＝sin(π/2)cos(-α)+cos(π/2)sin(-α)=1*cosα-0*sinα=cosα (sin(-α)=-sinα cos(-α)=cosα)

cos(π/2-α)=cos(π/2)cos(-α)+sin(π/2)sin(-α)=0*cosα+(-1)sin(-α)=sinα 手机打字太慢，请见谅