a是第四象限角,cos=3/5,则cos(a-π/4)是多少

问题描述:

a是第四象限角,cos=3/5,则cos(a-π/4)是多少

a是第四象限,且cosa=3/5,则sina=-4/5
cos(a-π/4)=cosacos(π/4)+sinasin(π/4)=(√2/2)[(3/5)+(-4/5)]=-√2/10