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Goal 11.6

Goal 11.6. Circumference of a Circle. Things you should know about circles. A circle i s the set of all points in a plane that are the distance from a fixed point called the center . The distance from the center to any point on the circle is the radius .

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Goal 11.6

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  1. Goal 11.6 Circumference of a Circle

  2. Things you should know about circles. • A circleis the set of all points in a plane that are the distance from a fixed point called the center. • The distance from the center to any point on the circle is the radius. • The distance across the circle through the center is the diameter.

  3. Find the circumference of the clock. Use 3.14 for π. C3.14(25) ≈ ANSWER The circumference of the clock is about 78.5 centimeters. EXAMPLE 1 Finding the Circumference of a Circle SOLUTION C=πd Write formula for circumference. Substitute 3.14 for π and 25 for d. =78.5 Multiply.

  4. 22 Find the circumference of the circle. Use forπ. 7 22 22 2 ≈ (21) C Substitute for π and 21 forr. 7 7 ANSWER The circumference of the circle is about 132 inches. EXAMPLE 2 Finding the Circumference of a Circle SOLUTION C= 2πr Write formula for circumference. =132 Multiply.

  5. 22 Find the circumference of the circle. Use or 3.14 for π. 7 3. 2. 1. ANSWER ANSWER ANSWER 628 cm 154 in. 56.52 mm for Example 2 and 3 GUIDED PRACTICE GUIDED PRACTICE GUIDED PRACTICE for Examples 1 and 2 GUIDED PRACTICE

  6. Giant Sequoias The largest living tree in the United States is a giant sequoia in Sequoia National Park in California. Its trunk is roughly circular and has a circumference of 1231 inches at ground level. What is the tree’s diameter at ground level? EXAMPLE 3 Finding the Diameter of a Circle

  7. 1231 3.14d = 3.14 3.14 392 d ≈ ANSWER 2 The tree’s diameter is about 392 inches, or 32 feet, at ground level. 3 12313.14d ≈ EXAMPLE 3 Finding the Diameter of a Circle SOLUTION C=πd Write formula for circumference. Substitute 1231 for C and 3.14 for π . Divide each side by 3.14 Simplify

  8. 4. Tree Limbs In Example 3, the circumference of the tree’s largest limb at its widest point is about 256 inches. Find its diameter. ANSWER about 81.5 in. for Example 2 and 3 GUIDED PRACTICE GUIDED PRACTICE GUIDED PRACTICE for Example 3 GUIDED PRACTICE

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