sin40=cos50 sin80=cos10所以2sin50+cos10(cos10+根号3sin10)/cos10=2sin50+2(1/2 cos10+根号3/2 sin10)注意到1/2=sin30 根号3/2=cos30=2sin50+2(sin30cos10+cos30sin10)=2sin50+2sin(30+10)=2sin50+2sin40根号下(1+...