Cho ∆DEF vuông tại D có , tia phân của cắt DF tại M, kẻ MN ^ EF
(N Î EF).
a) Tính số đo .
b) Chứng minh ∆EDM = ∆ENM.
c) ∆EDN là tam giác gì? Vì sao?
d) Biết ED = cm, MD = 3cm. Tính độ dài đoạn thẳng MF.
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