证明题(1949年南开大学

设人眼在墙顶上观察一塔,测得塔之全长所夹之角为θ,设墙高为h尺,墙与塔之距离为d尺.试证:(h²+d²)sinθ/(hsinθ+dcosθ)尺为塔这高.

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在 △ABC 中, cosC =2/3, AC = 4, BC = 3, 则 tanB =【 】

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在 △ABC 中, cosC = 2/3 , AC = 4, BC = 3, 则 cosB =【 】

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