Question

Write the standard form of the equation of the circle x^2+y^2+4x-2y-20=0. Find the center and radius.
How do I do this? pleaaase help.

Answer 1

complete square:

(x+2)^2+(y-1)^2 = 20

Then minus 2^2+1^2 = 5, so add 5 to the 20

we get (x+2)^2+(y-1)^2 = 25

sqrt 25 = 5

so, 5 is the radius

the center is at (x+2)^2 = 0

(y-1)^2 = 0

so x = -2

y = 1

so the center is at (-2,1)

Answer 2

thank you so much! ;)