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设□ABCD的底BC=a,高为h_a,则面积S=ah_a. 通常,课本和文献上的证法是:(1)如图1,作AE⊥BC,垂足
Let BCCD be the bottom BC=a, the height is h_a, then the area S=ah_a. Usually, textbook and literature proofs are: (1) As shown in Figure 1, for AE ⊥BC, foothold