The equation of a standard circle with centre at (a,b) and radius r is
(x-a)² + (y-b)² = r²
By inspection of the given circle,
(x+2)^2+(y-6)^2=16 and (x+2)^2+(y-6)^2=81
we conclude that both have centres at (-2,6), therefore they are concentric.
The radii of the circles are √16=4 and √81=9.
The area between the two circles are therefore
πr1²-πr2²
=π(9²-4²)
=65π
Garden Area Problem. A designer created a garden
from two concentric circles whose equations are as follows:
(x+2)^2+(y-6)^2=16 and (x+2)^2+(y-6)^2=81
The area between the circles will be covered with grass. What is the area of that section?
How do you do this?
3 answers
do you have any sites that explain this as well?
The subject should be in any pre-calc textbook. Alternatively, you can google
"equation of a circle".
"equation of a circle".
3 answers