Saturday

December 20, 2014

December 20, 2014

Posted by **rmz** on Friday, February 19, 2010 at 5:39pm.

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?

- Math -
**MathMate**, Friday, February 19, 2010 at 7:56pmThe 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

- Math -
**rmz**, Friday, February 19, 2010 at 8:13pmdo you have any sites that explain this as well?

- Math -
**MathMate**, Friday, February 19, 2010 at 8:25pmThe subject should be in any pre-calc textbook. Alternatively, you can google

"equation of a circle".

**Answer this Question**

**Related Questions**

ALGEBRA - The GARDEN AREA PROBLEM: A designer created a garden from two ...

Math - The dimensions of Mrs. Singleton's square garden are dilated using a ...

geometry - a target consists of five concentric circles, each with a radius 1 ...

math word problem - A rectangle garden is 30 ft by 40 ft. Part of the garden is ...

math - The lengths of the diameters of two concentric circles are 6 and 8. What ...

math - The Aesthetic Garden Problem. A landscape architect wants the length of ...

Math - Optimization Problem A right circular cylindrical can of volume 128tπ...

math - Given that a sports arena will have a 1400 meter perimeter and will have ...

11th grade Algebra II - Chad had a garden that was in the shape of a rectangle. ...

math - Joannies garden is in the shape of a square and has an area of 100 sq ft...