EXAMPLE 1 Use the formula for area of a circle Find the indicated measure. a. Area r = 2.5 cm SOLUTION Write formula for the area of a circle. = π (2.5)

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Presentation transcript:

EXAMPLE 1 Use the formula for area of a circle Find the indicated measure. a. Area r = 2.5 cm SOLUTION Write formula for the area of a circle. = π (2.5) 2 Substitute 2.5 for r. = 6.25π Simplify. ≈ Use a calculator. A = πr 2 The area of A is about square centimeters. ANSWER

EXAMPLE 1 Use the formula for area of a circle Find the indicated measure. A = cm 2 b. Diameter Write formula for the area of a circle. Substitute for A = πr 2 = r π Divide each side by π. 6 ≈ r Find the positive square root of each side. The radius is about 6 cm, so the diameter is about 12 centimeters. ANSWER A = πr 2 SOLUTION

EXAMPLE 2 Find areas of sectors Find the areas of the sectors formed by UTV. SOLUTION STEP 1 Find the measures of the minor and major arcs. Because m UTV = 70 °, mUV = 70 ° and mUSV = 360 ° – 70 ° = 290 °.

EXAMPLE 2 STEP 2 Find the areas of the small and large sectors. Area of small sector = πr 2 mUV 360 ° Write formula for area of a sector. = π ° 360 ° Substitute. ≈ Use a calculator. Find areas of sectors

EXAMPLE 2 = π ° 360 ° Substitute. ≈ Use a calculator. Find areas of sectors The areas of the small and large sectors are about square units and square units, respectively. ANSWER Write formula for area of a sector. Area of large sector = πr 2 mUSV 360 °

GUIDED PRACTICE for Examples 1 and 2 1. Area of D Use the diagram to find the indicated measure. about ft 2 ANSWER

GUIDED PRACTICE for Examples 1 and 2 2. Area of red sector Use the diagram to find the indicated measure. about ft 2 ANSWER

GUIDED PRACTICE for Examples 1 and 2 3. Area of blue sector Use the diagram to find the indicated measure. about ft 2. ANSWER