Area and Perimeter

What is the “area” of a shape? The amount of space occupied inside

the shape What is the “perimeter” of a shape? The total distance around the outside

of the shape

Review of Area

How do we calculate the area of: Square? Rectangle? Parallelogram?

Triangle? A square has equal sides so to calculate

the area A=s2

The area of a rectangle and parallelogram are calculated the same way – base x height or A=bh. For a parallelogram, the width is straight up, not the slant length.

The area of a triangle is half of dimensions of a rectangle. A = ½ bh

Review of Perimeter

How to calculate the perimeter of a square?

All sides are the same distance so P = 4xs

Perimeter of a rectangle There are two sets of matching sides so

P=2b + 2h

Perimeter of a parallelogram This is where the slant length is used. P = 2base + 2slant height

Perimeter of a triangle = add all 3 sides together

What about a circle??

What is a circle? Describe what a circle is.

A circle is a round shape with no beginning and no end. Its boundary is always the same distance away from a fixed point at its center

Calculations of Circles

To calculate the area and perimeter of a circle, it involves the measurements called the “radius” and “diameter”.

Both involve the center of the circle. The radius is the distance from the center to the edge of circle. The diameter is the distance across the entire circle from edge to edge, cutting through the center of the circle

Also involved in circle calculations is a term called “pi” (sounds like pie!). It’s symbol is

As a number, pi = 3.14159265359…, but for our use, 3.14 is good enough!

Area of a circle

The area of circle is pi x radius x radius or

Perimeter of a Circle

Perimeter of a circle is called the “circumference”

In circles the circumference is 3.14 (p) times the Diameter or 2 times the radius. Thus the formula looks like:2pr or pd.