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23、如图,四边形ABCD是菱形,对角线AC、BD相交于点O,DH⊥AB于点H,连接OH,求证:∠DHO=∠DCO.
24如图,已知四边形ABCD是平行四边形,DE⊥AB,DF⊥BC,垂足分别是E、F,并且DE=DF.求证:(1)△ADE≌△CDF;(2)四边形ABCD是菱形
25已知:如图所示,E是正方形ABCD边BC延长线一点,若EC=AC,AE交CD于点F,求∠AFC的度数.