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# Parabola Graph How To Answer watch

1. For this graph I have to find the equation in the form y = ax2 + bx + c but i don't know how to answer it .
Is it completing the square?
2. (Original post by ChocoholicCox)
For this graph I have to find the equation in the form y = ax2 + bx + c but i don't know how to answer it .
Is it completing the square?
You know two points on the curve (0.10) and (3,1) and you know that there is a minimum turning point when x=3.
This information should enable you to write down three simultaneous equations in a,b and c
3. (Original post by brianeverit)
You know two points on the curve (0.10) and (3,1) and you know that there is a minimum turning point when x=3.
This information should enable you to write down three simultaneous equations in a,b and c
I swear all you have to do is (x+3)2+ 1 = 0
then just multiply the brackets giving x2 + 6x + 9 then just plus the 1 giving x2 + 6x +10 because the x2​ shows its a parabola?
4. (Original post by ChocoholicCox)
I swear all you have to do is (x+3)2+ 1 = 0
then just multiply the brackets giving x2 + 6x + 9 then just plus the 1 giving x2 + 6x +10 because the x2​ shows its a parabola?
Wouldn't it be ? As 3 is the minimum (what makes the bracket equal 0)

You could also note right off the bat that as the graph crosses the y-axis at (0,10)
5. (Original post by Robbie242)
Wouldn't it be ? As 3 is the minimum (what makes the bracket equal 0)

You could also note right off the bat that as the graph crosses the y-axis at (0,10)
Yes, you can simply think of it as the standard parabola y=x^2, translated 3 units to the right and 1 unit upwards.
6. (Original post by brianeverit)
Yes, you can simply think of it as the standard parabola y=x^2, translated 3 units to the right and 1 unit upwards.
Yeah I know don't worry, I was just questioning the OPs deduction
7. (Original post by ChocoholicCox)
I swear all you have to do is (x+3)2+ 1 = 0
then just multiply the brackets giving x2 + 6x + 9 then just plus the 1 giving x2 + 6x +10 because the x2​ shows its a parabola?
Almost...

You have a vertex @ (3,1) and when x=0 y=10
The boxed equation is the quadratic equation in vertex form, where

Expand:

Can you see how you need to know what is before you go ahead and use that vertex equation? It just so happens that the y-intercept is 9, but if it was 4.5 or 20, then your value of would change and you'd have a slightly different equation...
8. (Original post by halpme)
Almost...

You have a vertex @ (3,1) and when x=0 y=10
The boxed equation is the quadratic equation in vertex form, where

Expand:

Can you see how you need to know what is before you go ahead and use that vertex equation? It just so happens that the y-intercept is 9, but if it was 4.5 or 20, then your value of would change and you'd have a slightly different equation...
oh right i see what u mean

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