f（x）=cos（-x/2)+sin(π-x/2）=cos(x/2)+sin(x/2)f(a)=cos(x/2)+sin(x/2)=（2√10）/5 cos(x/2)+sin(x/2)=（2√10）/5 平方 1+sina=8/5 sina=3/5 cosa=4/5 tana=3/4tan2a=2tana/(1-tan^2a)=24/7 tan（2a+π/4)=(1+...