∆ABC is an isosceles triangle with AB = AC = 15 cm

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∆ABC is an isosceles triangle with AB = AC = 15 cm and altitude from A to BC is 12 cm. The length of side BC is :

1. 9 cm.
2. 12 cm.
3. 18 cm.
4. 20 cm.

Correct Option: C

We draw a figure of an isosceles triangle ABC ,

Here , AB = AC = 15 cm.
AD ⊥ BC ; AD = 12 cm.
∴ BD = DC
In, ∆ABD
BD = √AB² - AD²
BD = √15² - 12²
BD = √(15 + 12)(15 – 12)
BD = √27 × 3 = 9 cm.
∴ BC = 2 × BD = 2 × 9 = 18 cm.