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數學M2題目trigo
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發問:
given that ABC is a triangle, cos A = sin B sin C Prove that ABC is a right-angled triangle!
最佳解答:
giventhat ABC is a triangle，CosA=SinBSinC，Prove that ABC is a right-angled triangle! Sol CosA=Cos(π－B－C)=－Cos(B+C)=SinBSinC－CosBCosC SinBSinC－CosBCosC=SinBSinC CosBCosC=0 CosB=0 orCosC=0 B=π/2 or C=π/2 So ABCis a right-angled triangle!
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