Question

[Trần Lan Phương]

Let ABC be a triangle with AB = 3cm, AC = 7cm. The internal bisector of the angle BAC intersects BC at D. The line passing through D and parallel to AC cuts AB at E. Find the measure of DE.
Answer: DE = ..........cm.

Write your answer by fraction in simplest form

Answer 1

[phan thế nghĩa]

ta có:

\(\frac{BD}{DC}=\frac{AB}{AC}=\frac{3}{7}\)( do AD là tia phân giác của \(\widehat{BAC}\))

\(\Rightarrow\frac{BD}{BC}=\frac{3}{11}\)

Ta có:

\(\frac{ED}{AC}=\frac{BD}{BC}=\frac{3}{11}\Rightarrow ED=\frac{3AC}{11}=\frac{3.7}{11}=\frac{21}{11}\)