SOLUTION: the area of a circular ring is 90. if the radius of the outer circle forming the ring is 7, what is the radius of the inner circle of the ring? (assume the circles forming the ring

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Question 258859: the area of a circular ring is 90. if the radius of the outer circle forming the ring is 7, what is the radius of the inner circle of the ring? (assume the circles forming the ring have the same center.)
Answer by Stitch(470) About Me  (Show Source):
You can put this solution on YOUR website!
The Area of a circle is 3.14%28Pi%29+%2A+R%5E2
The Area of the circular ring is the difference of the area of the larger circle minus the area of the inner circle.
Given: Radius of the outer circle is 7. The difference of the areas between the two circles is 90
Our Equation: 3.14%2A7%5E2+-+3.14%2AA%5E2+=+90
The left side of the equation can be simplified by dividing both terms by 3.14
3.14+%2A+%287%5E2+-+A%5E2%29+=+90
Divide both sides by 3.14
7%5E2+-+A%5E2+=+28.65
Simplify the equation
49+-+A%5E2+=+28.65
Add A^2 to both sides
49+=+28.65+%2B+A%5E2
Subtract 28.65 from both sides
20.35+=+A%5E2
Take the square root of both sides
highlight%284.5+=+A%29
The radius of the inner ring is 4.5