The perimeter of a triangle is the sum of the length of its three sides, whether they are equal or not.
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The area of a triangle is equal to the basis multiplied by the height divided by $$2$$.
$$$A=\dfrac{b \cdot h}{2}$$$
Semiperimeter of a triangle
The semiperimeter of a triangle is equal to the sum of its sides divided by $$2$$.
It is normally denoted with the letter p (in lower case) and we express it as:
$$$p= \dfrac{a+b+c}{2}$$$