ABC is a right angled triangle, right angled at A. A circle is inscribed in it. The lengths of two sides containing the right angle are 72 cm and 21 cm. The radius of the inscribed circle is:

9 cm

7, 24, 25 ⇒  21, 72, 75 (triplet)

Hence,

⇒ in-radius = \(\frac{AB\;+\;BC\;-\;AC}{2}\) = \(\frac{72+21-75}{2}\) = \(\frac{18}{2}\) = 9 cm