## selenamalter 2 years ago Write the equation of the parabola in vertex form. A. y = (x + 1)2 + 3 B. y = (x + 1)2 – 3 C. y = (x – 1)2 – 3 D. y = (x – 1)2 + 3

1. selenamalter

thats the wrong graph

2. ZeHanz

Do you see the zeroes at -1 and 4? The vertex is right in the middle of them: x = 1½. Also the y-coordinate of the vertex seems to be 7½. I cannot match it...

3. selenamalter

hold on let me get the other one

4. ZeHanz

Thought so... ;)

5. selenamalter

6. selenamalter

there

7. ZeHanz

What are the coordinates of the vertex?

8. selenamalter

um, (1,3)

9. selenamalter

?

10. ZeHanz

No, you have to go to the left and down... I get (-1, -3).

11. selenamalter

oh okay

12. ZeHanz

So if you look at the answer options, that doesn't help much: these same numbers are in every option, sometimes + sometimes -... You can find the right one by comparing this graph with that of the "father of all parabolas": y = x². That one has a vertex in (0, 0). So if x = 0, you get the other coodrinate of the vertex (also 0). In your parabola, you have to set x = -1 to get the vertex, so you get (x+1)² in the formula.

13. selenamalter

(x+1)^2+3

14. ZeHanz

That would be all, if the y-coordinate of the vertex was at y = 0, just as the vertex of y = x². But this isn't the case, it lies 3 units lower! OK, just subtract 3 from the formula, result: y = (x+1)²-3

15. ZeHanz

You added 3, which would make the parabola go 3 units up, instead of down...

16. selenamalter

okay, thank so much for all your help :D

17. ZeHanz

YW! Hope you understand the principle of moving the parabola.