Question

what is the radius of a circle with the equation x^2+y^2+2x+4y-9=0

Answer 1

standard form equation of the circle \[\huge\rm (x-h)^2+(y-k)^2=r^2\]
where (h,k) is the center point and r =radius

Answer 2

so move the -9 to the right side

Answer 3

do you know what a "perfect square trinomial" is?
sometimes also just called a "perfect square"

Answer 4

Yeah I heard of it.

Answer 5

\(x^2+y^2+2x+4y-9=0\\
x^2+y^2+2x+4y=9\\
x^2+2x+y^2+4y=9\\
(x+1)^2-1+y^2+4y=9\\
(x+1)^2+y^2+4y=10\)

Now do something similar with the \(y^2+4y\).

Answer 6

So I would get 3 for my answer correct?

Answer 7

Now look at what @Nnesha said

Answer 8

So my answer would be 6?

Answer 9

\(x^2+y^2+2x+4y-9=0\\
x^2+y^2+2x+4y=9\\
x^2+2x+y^2+4y=9\\
(x+1)^2-1+y^2+4y=9\\
(x+1)^2+y^2+4y=10\\
(x+1)^2+(y+2)^2-4=10\\
(x+1)^2+(y+2)^2=14\\
(x+1)^2+(y+2)^2=(\sqrt{14})^2\)

Answer 10

So my answer should be 3.74 correct ?

Answer 11

how did you get that?

Answer 12

I square rooted 14

Answer 13

right