Geometrymedium · Past Paper
What is the length of the radius of the circle x^2 + y^2 - 2x - 4y - 20 = 0?
A5
B20
Csqrt(20)
D25
✓ Correct Answer: A — 5
g = -1, f = -2, c = -20. r = sqrt(g^2 + f^2 - c) = sqrt((-1)^2 + (-2)^2 - (-20)) = sqrt(1+4+20) = 5.
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