答案解析

查看更多优质解析解答一举报正切二倍角公式:  tan2α = 2tanα/[1 - (tanα)^2]   tan(1/2*α)=(sin α)/(1+cos α)=(1-cos α)/sin α 推导:  tan(2a) = tan(a+a) = (tan(a) + tan(a))/(1 - tan(a)*tan(a) )= 2tanα/[1 - (tanα).

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