问题描述: 已知角α的正切值为b/a,求角α的正弦值和余弦值 1个回答 分类:数学 2014-11-28 问题解答: 我来补答 tanα=b/a,则(tanα)^2=b^2/a^2=(sinα)^2/(cosα)^2=[1-(cosα)^2]/(cosα)^2,可知,(cosα)^2=1/[1+(tanα)^2].最后求得:cosα=|根号下(1/[1+b^2/a^2)]|,同理,(tanα)^2=b^2/a^2=(sinα)^2/(cosα)^2=(sinα)^2/[1-(sinα)^2],可知,(sinα)^2=1+1/(tanα)^2.最后求得:sinα=|根号下(1+a^2/b^2)|.因为,a,b正负未知,所以要加上绝对值. 展开全文阅读