# LESSON 7.6 AREA AND CIRCUMFERENCE OF CIRCLES OBJECTIVE: To use formulas for the circumference and area of circles.

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LESSON 7.6 AREA AND CIRCUMFERENCE OF CIRCLES OBJECTIVE: To use formulas for the circumference and area of circles

DEFINITIONS is the set of all points that is a given distance from a given point. The given point is the of the circle. CENTER A CIRCLE

The given distance is the of the circle, which is a segment with one endpoint on the circle and the other at the center of the circle. RADIUS

is a segment, with both endpoints on the circle, that passes through the center of the segment. THE DIAMETER

One diameter equals two radii or d = 2r FORMULAS: Area of a circle Circumference of a circle A = π r 2 C = 2πr or C = πd

Find the circumference and the area. Leave π in the answer. 15 in C = πd C = 15π in. A = πr 2 A = π(7.5) 2 A = 56.25π in 2 Example #1

10 m C = 2 π r A = π r 2 C = 2(3.14)(10) C = 62.8m A = (3.14)(10) 2 A = 314m 2 Use 3.14 for π Example #2 Find the circumference and the area.

Example #3 If the circumference of a circle is 8π in., then find the area. First, we must find the radius. Then we will use the radius to find the area.

4 in = r 8 π = 2πr 2π 2π A = πr 2 A = π(4) 2 A = 16π in 2 C = 2πr Find the radius. Find the area.

Example #4 4. If the area of a circle is 113.04 m 2, then find the circumference. Use 3.14 for π. First, we must find the radius. Then we will use the radius to find C

A = πr 2 113.04 = (3.14)r 2 36 = r 2 6 m = r C = 2πr C = 2(3.14)(6) C = 37.68m Find the radius. Find Circumference

ASSIGNMENT: 7.6 Worksheet Show necessary work Minimum 3 lines

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