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duongvanphat2002
2 năm trước
Cho tứ diện ABCD có AB vuông góc BC,BD , tam giác BCD vuông tại C. Kẻ BE vuông góc với AC , EF vuông góc AC (F thuộc AD) . Chứng minh: a) CD vuông góc (ABC) b) BE vuông góc (ACD) c) EF vuông góc (ABC)
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