Shortcut Trick
For any right-angled triangle with perpendicular sides P, B and hypotenuse H, the radius of the incircle (inradius, r) is given by the direct formula:
r = (P + B − H) ÷ 2
Here, the sides are 14 cm, 48 cm, and 50 cm. Since 142 + 482 = 196 + 2304 = 2500 = 502, it is a right-angled triangle.
r = (14 + 48 − 50) ÷ 2 = 12 ÷ 2 = 6 cm
∴ The correct answer is 6 cm.
Alternate Method
Given:
Sides of the triangle: a = 14 cm, b = 48 cm, c = 50 cm
Formula Used:
Inradius of any triangle (r) = Area of triangle (A) ÷ Semi-perimeter (s)
Semi-perimeter (s) = (a + b + c) ÷ 2
Area of a right-angled triangle (A) = (1 ÷ 2) × Base × Height
Calculations:
First, verify if the triangle is right-angled:
⇒ 142 + 482 = 196 + 2304 = 2500
⇒ 502 = 2500
⇒ Since 142 + 482 = 502, the triangle is a right-angled triangle with base = 48 cm, height = 14 cm, and hypotenuse = 50 cm.
Now, calculate the semi-perimeter (s):
⇒ s = (14 + 48 + 50) ÷ 2
⇒ s = 112 ÷ 2 = 56 cm
Calculate the area of the triangle (A):
⇒ A = (1 ÷ 2) × 48 × 14
⇒ A = 24 × 14 = 336 cm2
Calculate the inradius (r):
⇒ r = A ÷ s
⇒ r = 336 ÷ 56
⇒ r = 6 cm
Option Analysis:
⇒ Option (1) - 5 cm: Incorrect, as the calculated inradius is 6 cm, not 5 cm.
⇒ Option (2) - 7 cm: Incorrect, as the calculated inradius is 6 cm, not 7 cm.
⇒ Option (3) - 8 cm: Incorrect, as the calculated inradius is 6 cm, not 8 cm.
⇒ Option (4) - 6 cm: Correct, as the calculated inradius is exactly 6 cm.
∴ The correct answer is 6 cm.
Additional Information
Circumradius of a Right-Angled Triangle
The circumradius (R) of a right-angled triangle is exactly half of its hypotenuse: R = Hypotenuse ÷ 2.
Inradius of an Equilateral Triangle
For an equilateral triangle of side a, the inradius is given by r = a ÷ (2 × √3).
Relation between Inradius and Circumradius
For any right-angled triangle, the relation between inradius (r), circumradius (R), and perpendicular sides (a, b) is given by: r = a + b − 2R.