I have a question, can anybody help me?
What is the general form of the equation of the given circle with center A?
http://cdn.ple.platoweb.com/PCAP-ASSETS-PROD/258cc385d685420384bc0a8b50aa8568
x2 + y2 + 6x − 24y − 25 = 0
x2 + y2 − 6x + 24y + 128 = 0
x2 + y2 + 6x – 24y + 128 = 0
x2 + y2 + 6x − 24y + 148 = 0

- anonymous

- jamiebookeater

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- anonymous

The equation of a circle with the center (h, k) and radius r is
\[(x-h)^2+(y-k)^2=r^2\]
Your center is (-3,12) so that's h and k. Your radius is 5. Plug in the numbers and expand the equation

- anonymous

(x-(-3)2 + (y-12)2 = 25 right?

- anonymous

yes

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## More answers

- anonymous

and what do i do next ? :s

- anonymous

foil (x+3)² and (y-12)²

- anonymous

is it (x+9) + (y + 144) = 25 ??

- anonymous

no. you need to use FOIL for both the x and y
(x + 3)² + (y - 12)² = 25
means
\[(x+3)(x+3)+(y-12)(y-12)=25\]

- anonymous

so it would be 6x and 24y right?

- anonymous

6x and -24y

- anonymous

okay so we can take out b and c in the answers right?

- anonymous

yes

- anonymous

is it a?

- anonymous

i don't know. I'm not actually working this problem. just following along to make sure your work is right. and now that I look it doesn't look like you can exclude both b and c yet

- anonymous

Ugh, i suck at math x.x

- anonymous

what did you get when you multiplied (x+3)(x+3)?
you've got to show me something so I can see where you're going wrong

- anonymous

6x and -24y

- anonymous

you couldn't have gotten just 6x and -24y. Show me the whole equation

- anonymous

once we got that part right I can show you how to simplify it into the form they want

- anonymous

so this is what I got with FOIL
(x-3) + (x-3) + (y-12) + (y-12) = 25

- anonymous

not sure if you have to multiply the 25 too..

- anonymous

ok. so FOIL is actually multiplication. it stands for First, Inner, Outer, Last. just to help you remember how to distribute. I'm going to show you (x - 3)(x - 3). |dw:1435246652683:dw|

- anonymous

ok. so FOIL is actually multiplication. it stands for First, Inner, Outer, Last. just to help you remember how to distribute. I'm going to show you (x + 3)(x + 3).
|dw:1435246844411:dw|

- anonymous

all those - should be + because our equation was (x + 3)(x + 3)

- anonymous

You try with (y -12)(|dw:1435246933731:dw|y-12)

- anonymous

y2 - 24y + 144

- anonymous

right. so the equation for the circle becomes
\[x^2+6x+9+y^2-24y+144=25\]

- anonymous

and you combine like terms right?

- anonymous

yes. don't forget to subtract the 25 from the right side since they want that side to be 0.

- anonymous

\[x ^{2} + y ^{2} -6x - 24y + 128 = 0\]

- anonymous

close. +6x :)

- anonymous

Yaaay!, omg you saved my life, thanks a lot n.n

- anonymous

no problem

- anonymous

can you help me out in another question? please ? :c

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