How to Find the Area of a Circle

Step-by-step solution

1. Write the area formula.

   $$A = \pi r^2$$

   Why: The area of a circle depends on the radius, not the diameter.

2. Substitute the radius.

   $$A = \pi (5)^2$$

   Why: The radius is 5.

3. Square the radius.

   $$A = 25\pi$$

   Why: 5 squared is 25. Keep pi for the exact answer.

4. Estimate with pi about 3.14.

   $$25 \times 3.14 \approx 78.5$$

   Why: The estimate helps you check the size of the answer.

Practice problems

Use the same method. Work each problem on paper, then open the answer to check.

1. 1

   $r = 3$

   Show answer

   $A = 9\pi$

2. 2

   $r = 10$

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   $A = 100\pi$

3. 3

   $r = 2$

   Show answer

   $A = 4\pi$

4. 4

   $r = 7$

   Show answer

   $A = 49\pi$

5. 5

   $r = 6$

   Show answer

   $A = 36\pi$