Q.AB and CD are two parallel straight lines. AD and BC intersect each other at point O. If OA = 2 cm, OB = 3 cm, and OD = 4 cm, then what is the length of OC? (a) 6 cm (b) 4 cm (c) 4.8 cm (d) 4.2 cm
Answer: A
Between triangles \( \triangle AOB \) and \( \triangle COD \): - \( \angle OAB \) = alternate angle \( \angle ODC \) [because AB \( \parallel \) CD] - \( \angle OBA \) = alternate angle \( \angle OCD \) [because AB \( \parallel \) CD] - \( \angle AOB \) = vertically opposite angle \( \angle COD \) ∴ Triangles \( \triangle AOB \) and \( \triangle COD \) are similar. ∴ \( \frac{OA}{OD} = \frac{OB}{OC} \) ⇒ \( \frac{2}{4} = \frac{3}{OC} \) ⇒ \( OC = \frac{12}{2} = 6 \) ∴ \( OC = 6 \) cm.
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