已知cosα＝1/7,cos（α-β）＝13/14,且0＜β＜α＜π/2,求sinβ

已知cosα＝1/7,cos（α-β）＝13/14,且0＜β＜α＜π/2,求sinβ
已知cosα＝1/7,cos（α-β）＝13/14,且0＜β＜α＜π/2,求sinβ

已知cosα＝1/7,cos（α-β）＝13/14,且0＜β＜α＜π/2,求sinβ
sina=4√3/7,cosa=1/7
sin(a-b)=3√3/14,cos(a-b)=13/14
sinb=sin(a-(a-b))=sinacos(a-b)-cosasin(a-b)=√3/2