已知π/6
问题描述：
已知π/6
答
π/6π/30cos(α-β)=12/13 sin(α-β)=5/13
cos(α+β)=-4/5 sin(α+β)=-3/5
sin(2α)=sin(α+β+α-β)=cos(α-β)sin(α+β)+sin(α-β)cos(α+β)
=(12/13)(-3/5)+(5/13)(-4/5)
=-56/65
答
π/6＜β＜α＜3π/4cos(α-β)=12/13所以0＜α-β＜π/2故sin(α-β)=√[1-(12/13)^2]=5/13sin(α+β)=-3/5所以π＜α+β＜3π/2那么cos(α+β)=-√[1-(-3/5)^2]=-4/5所以sin2α=sin[(α-β)+(α+β)]=sin(α-β)co...