FORMULABANK

Perimeter:

$$Perimeter = a + b + c

O: perimeter
a, b, c: side lengths

Area:
$\mathrm{Area}=\frac{1}{2}\cdot g\cdot h$

h: height
g: base

The height is always perpendicular to the base.
You can choose any side to be the base.

Example where the height is outside the triangle

Example where the height is inside the triangle

Example calculation that can be used for both cases above

$\frac{1}{2}\cdot 4\cdot 3=6$