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的半张角切线替换是用一个只由一半角的切线组成的公式代替一个给定表达式的部分或全部比值。
公式如下:
罪θ=1+棕褐色22θ2棕褐色2θ,因为θ=1+棕褐色22θ1−棕褐色22θ,棕褐色θ=1−棕褐色22θ2棕褐色2θ.
我们将用二倍角公式来证明:
罪θ棕褐色θ因为θ=2罪2θ因为2θ=因为22θ+罪22θ2罪2θ因为2θ=1+棕褐色22θ2棕褐色2θ,=1−棕褐色22θ2棕褐色2θ,=棕褐色θ罪θ=1−棕褐色22θ2棕褐色2θ1+棕褐色22θ2棕褐色2θ=1+棕褐色22θ1−棕褐色22θ.□
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