sin(a-b)sin(b-r)-cos(a-b)cos(r-b)
=-sin(a-b)sin(r-b)-cos(a-b)cos(r-b)
=-[cos(a-b)cos(r-b)+sin(a-b)sin(r-b)]
=-cos[(a-b)-(r-b)]
=-cos(a-b-r+b)
=-cos(a-r)
sin（a-b）sin（b-r）-cos（a-b）cos（r-b)
sin（a-b）sin（b-r）-cos（a-b）cos（r-b)
數(shù)學(xué)人氣：152 ℃時間：2020-06-02 18:59:04
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