Question

Which of the following is the correct graph of the ellipse?

Answer 1

Do you have the pictures of the ellipse?

Answer 2

Ah okay. You're gunna want to do something you probably haven't done since like algebra. Do you remember how to complete a square?

Answer 3

Not at all :/

Answer 4

Okay. I haven't done this in a while, so I might get this wrong once or twice, but we'll start with separating the x and the y

Answer 5

So you have 9x^2 -18x +y^2+4y+4 = 0

Answer 6

Which can be changed to

9(x^2-18x)+(y^2+4y) = -4

Answer 7

Oops 9(x^2-2x)+(y^2+4y)=-4

Answer 8

Okay, now if I remember correctly, completing a square you need to halve the number and then square it

Answer 9

So

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

Answer 10

You can take out the unnecesary parts

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

Answer 11

Which, doing some simple algebra, can be changed to

9*(x-1)^2 +(y+2)^2 = 9

Answer 12

So now we know that the center is at (1,-2)

Answer 13

So it's definitely one of the ones on the left.

Answer 14

You can divide by 9 on both sides to get a version that you're probably more familiar with

Answer 15

y?

Answer 16

(x-1)^2/1^2 + (y+2)^2/3^2 =1

Answer 17

Oh, that's just the way I learned it

Answer 18

I dunno if you've got a different equation.

Answer 19

no I mean is it y lol

Answer 20

Oh, is what y?

Answer 21

the answe lol

Answer 22

I mean, they're asking you to identify which parabola is the correct one, you technically don't even need the equation if you can do this in your head.

Answer 23

Or I mean, ellipse not parabola.

Answer 24

what do you think it is is?

Answer 25

Well you should be able to identify which one it is yourself. I've set up the more familiar version of the ellipse equation for you.

Answer 26

If you're still not getting it, maybe this site can help:

http://www.mathwarehouse.com/ellipse/equation-of-ellipse.php