问两个题:(1) 1/2sin15°-根号3/2sin75 (2)cos15°-sin15°/cos15°+sin15°(1)-根号2/2 (2)根号3/3

问题描述:

问两个题:(1) 1/2sin15°-根号3/2sin75 (2)cos15°-sin15°/cos15°+sin15°
(1)-根号2/2 (2)根号3/3

1)1/2sin15°-√3/2sin75
=cos60sin15-sin60cos15
=sin(15-60)
=sin(-45)
= -√2/2
(cos15°-sin15°)/(cos15°+sin15°) 同时除以 cos15
=(1-tan15)/(1+tan15)
=tan(45-15)
=tan30
=√3/3