原式=(1-cos20)/2+（1-coxs100)/2+sin10sin(10+40)
=1-1/2(cos20+cosx100)+sin10^2cos40+sin10cos10sin40
=````````````````````````````+cos40(1-cos20)/2+sin20sin40/2
=````````````````````````````+cos40/2-1/2(cos40cos20-sin40sin20)
=1-1/2(cos20+cos100)+cos40/2-1/2cos60
接下来再把再把cos100=-cos（20+60）带进去展开带进去算··········
别偷懒奥哦··