sin80-√3cos80-2sin20
=2sin(80-60)-2sin20
=2sin20-2sin20
=0sin80-√3cos80为啥化成2sin(80-60)了，不懂辅助角公式。。asinx+bcosx=√(a²+b²)sin(x+φ)(其中tanφ=b/a)