Building blocks

Perimeter

The perimeter is the total distance around the outside of a 2D shape. You calculate it by adding together all the lengths of a shape.

Following are some formulas for finding the perimeters of the most common polygons:


Equilareral triangle	Rectangle	Square
Perimeter=3(side) Perimeter=3s	Perimeter=2(length)+2(width) Perimeter=2l+2w	Perimeter=4(side) Perimeter=4s

A rectangle has a length of 5 centimeters and a width of 3 centimeters. Find the perimeter.

Solution 1: P = 5cm + 3cm + 5cm + 3cm = 16cm
Solution 2: P = 2(5cm) + 2(3cm) = 10cm + 6cm = 16cm

Find the value of x

P = 44 cm
x = ?

P= 2·base+2·height
44 = 2x+2·12
44=2x+24
44-24=2x
20=2x
10=x
Then x= 10 cm

Although a circle is not a polygon, sometimes we need to find the distance around the circle. This distance around the circle is called the circumference and is given by:

The radio of a circle is 2 inches. What is the circumference?

, that is C=2·3.14·2=12.56 inches