SOLUTION: The area of a circle is directly proportional to the square of its radius. The area of a circle whose diameter is 40 cm is 1256 sq cm. What is the area of a circle whose diameter i

Question 1004275: The area of a circle is directly proportional to the square of its radius. The area of a circle whose diameter is 40 cm is 1256 sq cm. What is the area of a circle whose diameter is 20 cm? 10 cm? 12 cm? 30 cm?
Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
Hi there,
The area of a circle is directly
proportional to the square of its radius.
A = kr^2
Where k = constant of proportionality
A = kr^2
1256 = k20^2
k = 1256/400
k = 3.14
Formula:
A = 3.14r^2
Problem:
A = 3.14 x 10^2
A = 3.14 x 100
A = 314 sq cm.
Hope this helps :-)
RELATED QUESTIONS
The area of a circle is proportional to the square of its radius. If the area of a circle (answered by Cromlix)

The are of a circle is directly proportional to the square of its radius. A circle with a (answered by Cromlix)

Perimeter of a circle is equal to the perimeter of a square whose area is 484 cm�. What... (answered by macston)

Find the area of a circle whose diameter is 80 cm. Use pi =... (answered by Alan3354)

if a circle has an area of 914 cm how long is the radius and... (answered by Alan3354)

Find the radius of a circle whose area is... (answered by liz2298)

calculate the area of a circle whose radius is... (answered by jim_thompson5910)

A circle has an area of 25 pie cm squared. If a circle was drawn within that circle the... (answered by Fombitz)