SOLUTION: A pleasant day to you Sir / Madam, please do help me with this direct square variation question, I am not sure of my answer. The area of a circle varies directly as the squ

Question 684629: A pleasant day to you Sir / Madam,
please do help me with this direct square variation question, I am not sure of my answer.
The area of a circle varies directly as the square of its radius. If the area is 78.5 when the radius is 5. Find the area when the radius is 8.
Thank you very much!
Answer by Jolliano(16) (Show Source): You can put this solution on YOUR website!
A = kr^2
where A = area
k = constant of variation/proportionality
r = radius.
When A = 78.5,r=5
Since
A = kr^2
78.5 =k *5^2 = 25k
k = 78.5/25 = 3.1
So,when r = 8,
A = 3.1 * 8^2
=3.1 * 64
=198.4cm^2
RELATED QUESTIONS
Dear Sir/ Madam a pleasant day! please help me with a word problem about joint variation, (answered by stanbon)

A pleasant day Sir/ Madam, please help me with this direct square variation problem.... (answered by Alan3354)

Dear Sir/Madam, A pleasant day to you! Can you please help me with this problem, I do (answered by solver91311)

A pleasant day to you Sir / Madam, please help me with these word problems about direct... (answered by MathLover1)

A pleasant day Sir/ Madam, my daughter has this problem in geometry and I am not good in... (answered by MathLover1)

Dear Sir/Madam, A pleasant day! Please help me with this problem on quadratic equation: (answered by Alan3354,josgarithmetic)

Sir/Madam, A pleasant day! please help me with this problem: Find the value of k so... (answered by nerdybill)

Dear Sir/ Madam, A pleasant day! can you please help me with this algebraic problem, (answered by solver91311)

A pleasant day Sir or Madam. please help me with this word problem involving rational... (answered by josmiceli)