tan((x+y)/2) = √6/2 tanx*tany=13/7 求cos(x-y)=

问题描述:

tan((x+y)/2) = √6/2 tanx*tany=13/7 求cos(x-y)=

用半角公式,把正切求出.把要求的余弦打开,代入正切值.(也可先化成余弦)