因为π/2＜β＜α＜3π/4,cos(α-β)=12/13,sin(α+β)=-3/5所以,sin(α-β)=5/13,cos(α+β)=-4/5那么sin2α=sin(α+β+α-β)=sin(α+β)*cos(α-β)+sin(α-β)*cos(α+β)=-3/5*12/13+5/13*(-4/5)=-56/65...