Cho ∆DEF vuông tại D có, tia phân của cắt DF tại M

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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