Perimeter
Perimeter is the continuous line forming the boundary of a closed geometric figure(shape). Perimeter is often measured by measuring the outsides of a figure. Here are some commonly used equations for perimeter (x = multiplication):
Circle: 2 x π x radius
Rectangle: 2(l x w)
Square: 4 x a (a = sides)
Parallelogram: 2(a+b)
Triangle: a + b + c
Trapezoid: a + b + c + d