# Solution for plotting a quadratic graph from an equation

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#1
Hi! I have been looking at some extra questions for maths and I came up with a solution for this problem, but I am not sure if it is right or not. I had to sketch out a graph for the equation y=x^2+2x-3... Can someone please help me with this?
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#2
Here is a photo of the solution I came up with... I am not sure if it is correct
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1 month ago
#3
(Original post by MayaVellichor)
Here is a photo of the solution I came up with... I am not sure if it is correct
Did it tell you to complete the square? Are you in Year 12?
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1 month ago
#4
(Original post by MayaVellichor)
Hi! I have been looking at some extra questions for maths and I came up with a solution for this problem, but I am not sure if it is right or not. I had to sketch out a graph for the equation y=x^2+2x-3... Can someone please help me with this?
Yes, it's correct. Your approach is fine, although you should be able to factorise it by inspection, then assert that the minimum (/ maximum for negative x^2 coefficients) is at the average of the two roots' x coordinates.
Last edited by RogerOxon; 1 month ago
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#5
(Original post by Muttley79)
Did it tell you to complete the square? Are you in Year 12?
No year 10
Last edited by MayaVellichor; 1 month ago
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#6
(Original post by RogerOxon)
Yes, it's correct. Your approach is fine, although you should be able to factorise it by inspection, then assert that the minimum (/ maximum for negative x^2 coefficients) is at the average of the two roots' x coordinates.
OK... Thank you!
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#7
(Original post by MayaVellichor)
No year 10
I was just doing it for some fun
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1 month ago
#8
(Original post by MayaVellichor)
No year 10
OK - factosing to find the roots is much quicker, Never complete the square unless you are told to.

The x-coord of the turning point is the mean of the roots - then you can substitute to find the y coord. You can see the intersection on the y-axis by inspection.
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#9
(Original post by Muttley79)
OK - factosing to find the roots is much quicker, Never complete the square unless you are told to.

The x-coord of the turning point is the mean of the roots - then you can substitute to find the y coord. You can see the intersection on the y-axis by inspection.
Thank you! I will bare that in mind next time!
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1 month ago
#10
This website is great for checking graphs - https://www.desmos.com/calculator

Type in the function using the 'x' key on your keyboard
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#11
(Original post by hw8)
This website is great for checking graphs - https://www.desmos.com/calculator

Type in the function using the 'x' key on your keyboard
Thank you!
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1 month ago
#12
(Original post by MayaVellichor)
Thank you! I will bare that in mind next time!
If you take A level you will learn another way of finding turning points which is why I asked which year you were in
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1 month ago
#13
Use the quadratic formula and you can never go wrong.
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#14
(Original post by Muttley79)
If you take A level you will learn another way of finding turning points which is why I asked which year you were in
Is it something to do with (-p, q) or is it something completely different?
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1 month ago
#15
I'm assuming they are talking about differentiation.
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#16
(Original post by FrankishEmpire)
I'm assuming they are talking about differentiation.
Cool! Thanks! I will definitely look into that...
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1 month ago
#17
(Original post by MayaVellichor)
Is it something to do with (-p, q) or is it something completely different?
It's calculus - specifically differentiation which can find the gradient and turning points of curves.
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1 month ago
#18
It's basically a speedrun tactic. Integration is useful for finding areas too if you want to learn more about that.
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1 month ago
#19
(Original post by FrankishEmpire)
Use the quadratic formula and you can never go wrong.
That is NOT good advice when the x^2 coord is 1 and c is prime; it takes much longer.
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1 month ago
#20
(Original post by MayaVellichor)
Cool! Thanks! I will definitely look into that...
Wait until you are taught it ...
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