The area of a circle varies directly as the square of its radius. A circle with radius 2 in. has area 12.568 in. squared. What is the area of a circle with radius 5.7 ​in.?

1 answer

The area \( A \) of a circle is given by the formula:

\[ A = k r^2 \]

where \( k \) is the constant of proportionality, and \( r \) is the radius of the circle.

From the information provided, we know that for a circle with a radius of 2 inches, the area is 12.568 square inches. We can use this information to find \( k \).

Substituting the values we have:

\[ 12.568 = k \cdot (2^2) \]

\[ 12.568 = k \cdot 4 \]

Solving for \( k \):

\[ k = \frac{12.568}{4} = 3.142 \]

Now that we have the value of \( k \), we can find the area of a circle with a radius of 5.7 inches.

Using the formula again:

\[ A = k r^2 \]

Substituting \( k = 3.142 \) and \( r = 5.7 \):

\[ A = 3.142 \cdot (5.7^2) \]

Calculating \( 5.7^2 \):

\[ 5.7^2 = 32.49 \]

Then substituting back into the area formula:

\[ A = 3.142 \cdot 32.49 \approx 102.12658 \]

Thus, the area of a circle with a radius of 5.7 inches is approximately \( 102.13 \) square inches.