问题描述: 已知sin(α+β)sin(α-β)=3分之1 求cos2β-cos2α的值,4分之1 sin2α方+sinβ方+cosα4次方的值 1个回答 分类:数学 2014-11-14 问题解答: 我来补答 解cos2β-cos2α=cos[(a+β)+(β-α)]-cos[(β+α)-(β-α)]=cos(a+β)cos(β-α)-sin(a+β)sin(β-α)-cos(a+β)cos(β-α)-sin(a+β)sin(β-α)=-2sin(α+β)sin(β-α)=2sin(α+β)sin(α-β)=2/3(sin2α)^2/4+(sinβ)^2+(cosα)^4=(sin2α)^2/4+(1-cos2β)/2+(1/2+cos2α/2)^2=(sin2a)^2/4+(1-cos2β)/2+1/4+(cos2α)^2/4+cos2α/2=1+1/4+1/2-(cos2β-cos2α)/2=7/4-(1/3)=17/12 展开全文阅读