若tanα=m 则sin(-5π-α)cos(3x+α)=

问题描述:

若tanα=m 则sin(-5π-α)cos(3x+α)=

sin(-5π-α)cos(3π+α)
=sina*(-cosa)
=-sinacosa
=-sinacosa/(sin^2a+cos^2a) 分子分母同时除以 cos^2a
=-tana/(1+tan^2a) tanα=m
=-m/(1+m^2)