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student3
2 năm trước
Cho tam giác abc cân tại a . kẻ ah vuông góc bc( (h thuộc bc) a. Chứng minh ∆ ahb=∆ahc và hb=hc b. Hd vuông góc ab ( d thuộc ab) . he vuông góc ac ( e thuộc ac) . chứng minh hd=he c.Nếu góc a=120° thì ∆HDE là tam giác gì ? Vì sao? Giúp mình nha . mình cám ơn nhiều
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