Need help with finding the center radius form of the circle 9x^+9y^+18y-12y-131=0. I can work these out when I can factor out the same number but, this one is giving me trouble.

Alan

Need help with finding the center radius form of the circle 9x^+9y^+18y-12y-131=0. I can work these out when I can factor out the same number but, this one is giving me trouble.

Alan

Alan

- stapel_eliz
**Posts:**1686**Joined:**Mon Dec 08, 2008 4:22 pm-
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I made a typo, sorry. If I rearrange it to read 9x^+18x+9y^-12y=131 I know I need to factor out a number before completing the square on both sides, but if I factor out a 3 it's got me confused.

Example: 4x^+12x+4y^+24y-99=0 move the 99 and factor out a 4, then complete the square both sides

4(x^+3x+9/4)+4(y^+6y+9)=99+4(9/4)+4(9)

4(x+3/2)^+4(y+3)^=144 divide both sides by 4

(x-3/2)^+(y+3)^=36

(-3/2,-3) radius 6

The first example just isn't working out for me.

Example: 4x^+12x+4y^+24y-99=0 move the 99 and factor out a 4, then complete the square both sides

4(x^+3x+9/4)+4(y^+6y+9)=99+4(9/4)+4(9)

4(x+3/2)^+4(y+3)^=144 divide both sides by 4

(x-3/2)^+(y+3)^=36

(-3/2,-3) radius 6

The first example just isn't working out for me.

- stapel_eliz
**Posts:**1686**Joined:**Mon Dec 08, 2008 4:22 pm-
**Contact:**

That's where I'm having a problem. You can't factor out 9 because of the -12y. This problem isn't working out just as the other one I gave as an example.

Alan

Alan

- stapel_eliz
**Posts:**1686**Joined:**Mon Dec 08, 2008 4:22 pm-
**Contact:**