求证cosA/(tanA/2-cotA/2)=-1/2sinA

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求证cosA/(tanA/2-cotA/2)=-1/2sinA
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求证cosA/(tanA/2-cotA/2)=-1/2sinA
求证cosA/(tanA/2-cotA/2)=-1/2sinA

求证cosA/(tanA/2-cotA/2)=-1/2sinA
tanA/2-cotA/2=sin(A/2)/cos(A/2)-cos(A/2)/sin(A/2)
通分 =sin(A/2)的平方-cos(A/2)的平方/sin(A/2)cos(A/2)
=-cosA/[1/2sin(A/2)]
将tanA/2-cotA/2=-cosA/[1/2sin(A/2)]
代入原式=cosA/[-cosA/[1/2sina(A/2]
化简得-SIN(A/2)