Question

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

Answer 1

thats the wrong graph

Answer 2

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...

Answer 3

hold on let me get the other one

Answer 4

Thought so... ;)

Answer 5

there

Answer 6

What are the coordinates of the vertex?

Answer 7

um, (1,3)

Answer 8

?

Answer 9

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

Answer 10

oh okay

Answer 11

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.

Answer 12

(x+1)^2+3

Answer 13

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

Answer 14

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

Answer 15

okay, thank so much for all your help :D

Answer 16

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