1.证明tanx+tany=tan(x+y)-tanxtanytan(x+y)
2.求tan20度+tan40度+根下3倍tan20度tan40度
人气：369 ℃ 时间：2020-06-06 18:49:11
解答
tan(x+y)=(tanx+tany)/(1-tanxtany)
整理得tanx+tany=tan(x+y)-tanxtanytan(x+y)
tan20+tan40+√3tan20tan40
＝tan60-tan60tan20tan40+√3tan20tan40
=tan60=√3
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