NDA 2019 Maths · Mathematics · Properties of Triangles · easy

The inradius of a triangle with sides 9, 40 and 41 is

Single correct option

The inradius of a triangle with sides

9

40

and

41

Show answer and solution

Answer: (A) $4$

s=45

and, by Heron's formula, area

=\sqrt{45\cdot36\cdot5\cdot4}=180

(the triangle is right-angled:

9^2+40^2=41^2

). Inradius

r=\frac{\text{area}}{s}=\frac{180}{45}=4

. Option

6

comes from using half the perimeter incorrectly as

30

Original question written in the NDA 2019 Maths pattern and checked twice for the correct answer. Not an official question paper. How we write and check questions · Corrections policy · Report a mistake