Perimeter of a parallelogram

The perimeter of a parallelogram is the sum of the lengths of all four of its sides. A parallelogram is a shape similar to a rectangle, but with two opposite sides slanted, as you can see in the diagram below. Even so, the sides always come in two pairs of equal length. Let the lengths of two different sides be a and b. Then the perimeter of the parallelogram, which we denote P, is

$$P=2\cdot a+2\cdot b$$

The parallelogram below has side lengths a = 4 and $b=\sqrt{5}$, so its perimeter is

$$P=2\cdot 4+2\cdot \sqrt{5}=8+2\sqrt{5}$$

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