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An isosceles triangle has perimeter $ 30 \mathrm{~cm} $ and each of the equal sides is $ 12 \mathrm{~cm} $. Find the area of the triangle.
Given:
An isosceles triangle has perimeter $30\ cm$ and each of the equal sides is $12\ cm$.
To do:
Let us assume the third side of the triangle as $x$
We have,
Two sides with equal length of $12\ cm$
and perimeter as $30\ cm$
We know that,
Perimeter $P$ of a triangle with sides of length $a\ units, b\ units$ and $c\ units$
$P=(a+b+c)\ units$.
This implies,
$30\ cm=12\ cm+12\ cm+x\ cm$
$30\ cm=24\ cm+x\ cm$
This implies,
$x\ cm=30\ cm-24\ cm$
$x\ cm=6\ cm$
By Heron's formula:
$A=\sqrt{s(s-a)(s-b)(s-c)}$
Since,
$S=\frac{a+b+c}{2}$
$S=\frac{12+12+6}{2}$
$S=\frac{30}{2}$
$S=15\ cm$
This implies,
$A=\sqrt{15(15-12)(15-12)(15-06)}$
$A=\sqrt{15(3)(3)(9)}$
$A=9\sqrt{15}\ cm^2$
Therefore,
The area of the triangle is $9\sqrt{15}\ cm^2$.
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