Question

What's the formula to perimeter

Answer 1

The formula is:

Perimeter = (the distance all the way around the outside of the figure) .

How to calculate the distance all the way around the outside of the figure
is different for every shape.

A few of them are:

Square . . . . . 4 x the length of one side

Rectangle . . . . . (2) x (length + width)

Circle . . . . . (2 pi) x (radius)

etc.

Answer 2

$The\ perimeter\ of\ any\ polygon\ is\ the\ sum\ of\ the\ lengths \\of\ all\ its\ sides\ (a,\ b,\ c,\ d,\ ...)\\\\triangle:\ \ \ P=a+b+c\\\\equilateral\ triangle:\ \ \ P=3a \\\\rectangle:\ \ \ P=2a+2b \\\\square:\ \ \ P=4 a\\\\diamond :\ \ \ P=4a\\\\trapez:\ \ \ P=a+b+c+d\\\\isosceles trapezoid:\ \ \ P=a+b+2c\ \ \ \ \ (c-arm length)\\\\any\ polygon:\ \ \ P=a+b+c+d+...\\----------------\\The\ perimeter\ of\ a\ circle:\ \ \ P=2 \pi r\ \ \ \ \ (r-radius\ or\ a\ circle)$