### Home > CC2MN > Chapter 10 > Lesson 10.2.2 > Problem10-43

10-43.

The circle shown at right has a diameter of $20$ cm.

1. What measurement do you need to find in order to calculate the area inside the circle?

Recall the equation for area from the Math Notes box in this lesson.
$A=r^2\pi$

What measurement is missing in this equation?

2. Find the area inside the circle using the formula $A=r^2\pi$. Write your answer as a product of $r^2$ and $\pi$, and as an approximation using $\pi=3.14$.

Solve for $r$.

$20=2r$

Substitute the newly calculated radius into the area formula.

$A=(10)^2\pi$

$314$ cm2
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