Question

In triangle ABC , Angle B =90° , AB =5cm and AC = 13cm then BC = ?

Answer 1

it is a right angle triangle, so we can apply Pythagoras' theorem:

a² + b² = c²

5² + BC² = 13²

BC² = 13² - 5²

BC² = 144

BC = √144

BC = 12

Answer: (2) 12 cm

Answer 2

In ΔABC right angled at B,

By Pythagoras Theorem,

(AC)² = (AB)² + (BC)²

⇒ 13² = 5² + (BC)²

⇒ 169 = 25 + BC²

$=> BC = \sqrt{169 - 25}$

$=> BC = \sqrt{144}$

$=> BC = {\sqrt{(12)^2}$

or,

$BC = 12 units$