题目内容

已知向量a=（cosα，sinα），向量b=（cosβ，sinβ），|a-b|=2根号5/5 1.求cos（α-β）的值； 2.若-π/2＜β＜0＜α＜π/2，sinβ=-5/13，求sinα的值。

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