SOLUTION: Find the radius of a circle with an area of 100in^2 (using quadratic equations)

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Question 1194390: Find the radius of a circle with an area of 100in^2 (using quadratic equations)
Found 2 solutions by ikleyn, MathTherapy:
Answer by ikleyn(52778) About Me  (Show Source):
You can put this solution on YOUR website!
.

    pi%2Ar%5E2 = 100  in^2  is your area equation, with the unknown radius "r".


From this equation.

    r%5E2 = 100%2Fpi

and

    r = sqrt%28100%2Fpi%29 = sqrt%28100%2F3.14159%29 = use your calculator = 5.642  inches  (rounded).    ANSWER

Solved.



Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!
Find the radius of a circle with an area of 100in^2 (using quadratic equations)
Quadratic equation formula? WHY?
Anyway, we get: 

Quadratic equation formula: matrix%281%2C3%2C+r%2C+%22=%22%2C+%28-+b+%2B-+sqrt%28b%5E2+-+4ac%29%29%2F%282a%29%29, where: matrix%283%2C3%2C+a%2C+%22=%22%2C+pi%2C+b%2C+%22=%22%2C+0%2C+c%2C+%22=%22%2C+100%29

Should be pretty easy for you to substitute and calculate to find your answer, after IGNORING the negative value.