Math 6 Honors Periods 6 & 7

Area of Circles 10-3

Recall that there are two formulas for the circumference C of a circle. If the diameter of the circle is denoted by d and the radius by r, then

C =πd and C = 2πr

Two approximations for the number π are 3.14 and

The part of the plane enclosed by a circle is called the area of the circle.

Formula

Area of circle = π · (radius)²

A = πr²

Find the area of the shaded regions. Use π ≈ 3.14

Recall that we give answers to only three digits when we use the approximation π≈ 3.14. In fact, sometimes to avoid approximation we give the answer in terms of π.

Find the area of the shaded region. Leave your answer in terms of π

(Look at your textbook for examples)

Area of shaded region = Area of large circle – Area of small circle.

We must first find the area of the small circle.

A = πr² = π2² = 4π

We then find the area of the large circle. Since the radius of the large circle is the same as the diameter of the small circle we know that the radius of the circle must be 4 m so A = πr² = π4²= 16π

Thus, the area of the shaded region is equal to 16π - 4π = 12π