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 6.2 ​in.?

1 answer

To determine the area of a circle with a radius of 6.2 inches, we start with the formula for the area of a circle:

\[ A = k r^2 \]

where \( A \) is the area, \( r \) is the radius, and \( k \) is the constant of variation.

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

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

Calculating \( 2^2 \):

\[ 2^2 = 4 \]

Now we can plug this into our equation:

\[ 12.568 = k \times 4 \]

To find \( k \), we divide both sides by 4:

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

Now that we have the value of \( k \), we can find the area of the circle with a radius of 6.2 inches:

\[ A = k (6.2^2) \]

Calculating \( 6.2^2 \):

\[ 6.2^2 = 38.44 \]

Now substitute \( k \) and \( 6.2^2 \) back into the area formula:

\[ A = 3.142 \times 38.44 \]

Calculating the product:

\[ A \approx 3.142 \times 38.44 \approx 120.634 \]

Thus, the area of the circle with a radius of 6.2 inches is approximately:

\[ \boxed{120.634} \text{ square inches.} \]