Perimeter and area of a triangle

The perimeter of a triangle is the sum of the length of its three sides, whether they are equal or not.

The area of a triangle is equal to the basis multiplied by the height divided by $2$.

$$A={\displaystyle \frac{b\cdot h}{2}}$$

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:

$$p={\displaystyle \frac{a+b+c}{2}}$$