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

Answer 1

(a) 5.6 cm
$\because$ DE ∥ BC

$$\begin{gathered} \therefore \frac{AD}{AB}=\frac{AE}{AC}=\frac{DE}{BC}(\mathrm{Thales}\text{'}\mathrm{theorem}) \\ \Rightarrow \frac{3.5}{AB}=\frac{5}{8} \\ \Rightarrow AB=\frac{3.5\times 8}{5}=5.6\mathrm{cm} \end{gathered}$$