1.sin7°+cos15°sin8°/cos7°-sin15°cos8°=
1.sin7°+cos15°sin8°/cos7°-sin15°cos8°=
2.已知π/2<β<3π/4,cos(α-β)=12/13,sin(α+β)=-3/5,求sin2α的值.
3.已知sin(2α+β)+2sinβ=0,求证tanα=3tan(α+β)
4.已知向量a=(cosα,sinα) b=(cosβ,sinβ),|向量a-向量b|=2√2/5
(1)求cos(α-β)的值.
(2)若0<α<π/2,-π/2<β<0,且sinβ=-5/13,求sinα