Question

Calculate the radius of a circle by completing the square of the equation x2 + y2 −16x −10y +40 =0.(1 point)

-7

6

7

4

Answer 1

Complete the square:

x^2 − 16x = (x − 8)^2 − 64
y^2 − 10y = (y − 5)^2 − 25

So
(x − 8)^2 − 64 + (y − 5)^2 − 25 + 40 = 0
=> (x − 8)^2 + (y − 5)^2 = 49

Thus the radius = sqrt(49) = 7.

Answer: 7.