The perimeter of a triangle whose two sides are 18 cm and 10 cm is 42 cm. Find the area of the triangle.

$21\sqrt{11} cm^2$

3rd side of triangle = 42 - 18 - 10 = 14

Semiperimeter of triangle (S) = \(\frac{42}{2}\) = 21

Area of triangle = \(\sqrt { S ( S - a) (S - b ) (S - c) }\)

= \(\sqrt { 21 × 7 × 11 ×3  }\)

= 21\(\sqrt {  11  }\)

The correct answer is Option (1) → $21\sqrt{11} cm^2$