Question:
In the given figure, DE ∥ BC. If DE = 5 cm, BC = 8 cm and AD = 3.5 cm, then AB = ?
(a) 5.6 cm
(b) 4.8 cm
(c) 5.2 cm
(d) 6.4 cm
Solution:
(a) 5.6 cm
$\therefore \frac{A D}{A B}=\frac{A E}{A C}=\frac{D E}{B C} \quad$ (Thales' theorem)
$\Rightarrow \frac{3.5}{A B}=\frac{5}{8}$
$\Rightarrow A B=\frac{3.5 \times 8}{5}=5.6 \mathrm{~cm}$