2dao数学题

1、sin20*cos70+sin10*sin50
=1/2(sin90-sin50)-(1/2)(cos60-cos40)
=1/2(1-sin50-cos60+cos40)
=1/2(1-1/2)
=1/4
2、(sin7+cos15*sin8)/(cos7-sin15sin8)
=(sin7+1/2(sin23-sin7))/(cos7+1/2(cos23-cos7))
=(sin23+sin7)/(cos23+cos7)
=2sin15cos8/2cos15cos8
=tan15
=2-√3

1. ≈0.16
2. ≈0.27
(sin20≈0.3420201433;cos70≈0.3420201433
sin10≈0.1736481777;sin50≈0.7660444431
sin7≈0.1218693434;cos15≈0.9659258263
sin8≈0.139173101;cos7≈0.7725461516
sin15≈0.2588190451)