f(x)=sin2x/2f'(x)=cos2xx=π/4 f(π/4)=1/2 f'(π/4)=0f(x)-1/2=f'(π/4)(x-π/4)切线方程f(x)-1/2=0
f(x)的导数=cosx cosx+sinx (-sinx)=cosx2-sinx2=cos2x这就是切线方程。。再把x的值代入,就噢啦