Question

sinx cosx tanx 都能用tanx/2表示

Answer 1

1.

sinx=sin(x/2+x/2)=2sinx/2cosx/2=(2sinx/2cosx/2)/(sin^2x/2+cos^2x/2)=2tanx/2/(1+tan^2x/2);

2.

cosx=cos(x/2+x/2)=cos^2x/2-sin^2x/2=(cos^2x/2-sin^2x/2)/(sin^2x/2+cos^2x/2)=(1-tan^2x/2)/(1+tan^2x/2);

3.

tanx=sinx/cosx=2tanx/2/(1-tan^2x/2)

给分吧~：）