Question

What is the radius of the circle shown below?
x^2+y^2-8x-10y-8=0

Answer 1

I've gotten 7 - is that correct?

Answer 2

you need to complete the square for both x and y

\[x^2 - 8x + y^2 - 10y = 8\]

(-8/2)^2 = 16 (-10/2)^2 = 25

add 16 and 25 to both sides

\[x^2 - 8x + 16 + y^2 - 10y + 25 = 8 + 16 + 25\]

factorise

\[(x -4)^2 +(y - 5)^2 = 7^2\]

the radius is 7

Answer 3

Thanks!

Answer 4

hope it helps