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統計： A(11), B(17), C(11), D(69), E(0) #296405

詳解 (共 1 筆)

#924383
設BC長x
由餘弦定理:cosA = (b^2 + c^2 - a^2) / 2bc 
=> 0.5 = (41-x^2) / 40
=> x^2 = 21
=> x = 根號21(負不合)
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