已知sina=-3/5,a是第四象限角,求sin(π/4-a),cos(π/4+a),tan(a-π/4)的值
<p>问题：已知sina=-3/5,a是第四象限角,求sin(π/4-a),cos(π/4+a),tan(a-π/4)的值<p>答案：↓↓↓<p class="nav-title mt10" style="border-top:1px solid #ccc;padding-top: 10px;">陈智峰的回答：<div class="content-b">网友采纳 a是第四象限角,cosa=4/5,tana=-3/4 sin(π/4-a)=sinπ/4cosa-cosπ/4sina=7√2/10 cos(π/4+a)=cosπ/4cosa-sinπ/4sina=7√2/10 tan(a-π/4)=(tana-tanπ/4)/(1+tanatanπ/4)=-7
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