Question

Find the area of a triangle in cm${}^2$; whose sides are: $21cm,28cm$ and $35cm$.

Answer 1

Area of triangle with sides a, b, and c
s$=\frac{a+b+c}{2}$ is $\sqrt{s(s-a)(s-b)(s-c)}$.
For triangle with sides 21 cm, 28 cm and 35 cm,

$s=\frac{21+28+35}{2}=42cm$
Area of the triangle $=\sqrt{42(42-21)(42-28)(42-35)}$

$=\sqrt{42\times 21\times 14\times 7}$

$=\sqrt{21\times 2\times 21\times 7\times 2\times 7}$

$=21\times 7\times 2=294{cm}^2$