How do I graph these Quadratic functions?

Chart21

New member
Joined
May 2, 2021
Messages
3
1. f(x) = -1/19x2

Not sure what to do. If this was f(x) = 5x2 I'd do (0,0) as the vertex and make a table to figure out some other points. But I'm really stuck with this super odd fraction. A video told me to use a number that, when squared, is divisible by the fractions denominator. 19 squared is 361! I can't even graph that on my homework. I've also tried using a table and some fractions, but the rise/run fraction works when you don't have an x value already. I'm just really stuck here.

2. f(x) = 2(x-11)2

I know that the vertex is (11, 0). How do I calculate the y value?

Graphing f(x) = a(x-h)^2 is super hard for me. I've looked everywhere online and no one explains it. When I try solving it by using FOIL to turn it into general form, it's wrong. So obviously there's a way to solve these that isn't using general form.
 

Subhotosh Khan

Super Moderator
Staff member
Joined
Jun 18, 2007
Messages
24,624
1. f(x) = -1/19x2

Not sure what to do. If this was f(x) = 5x2 I'd do (0,0) as the vertex and make a table to figure out some other points. But I'm really stuck with this super odd fraction. A video told me to use a number that, when squared, is divisible by the fractions denominator. 19 squared is 361! I can't even graph that on my homework. I've also tried using a table and some fractions, but the rise/run fraction works when you don't have an x value already. I'm just really stuck here.

2. f(x) = 2(x-11)2

I know that the vertex is (11, 0). How do I calculate the y value?

Graphing f(x) = a(x-h)^2 is super hard for me. I've looked everywhere online and no one explains it. When I try solving it by using FOIL to turn it into general form, it's wrong. So obviously there's a way to solve these that isn't using general form.
I think you have an "aversion" towards plotting decimals. Get over it !! Just scale the y-axis appropriately and plot. The problem (1) will look as follows:

x​
f(x)​
0​
0​
-1​
0.052632​
1​
0.052632​
-2​
0.210526​
2​
0.210526​
-3​
0.473684​
3​
0.473684​

1619974441528.png

Now show us your work for the second problem! For that problem - I would choose x = 11, 10, 12, 9, 13 (symmetrical about the vertex x = 11)
 

Chart21

New member
Joined
May 2, 2021
Messages
3
Our teacher said she specifically doesn't want to teach us how to graph with decimals because it's too complicated. I guess I'll go find tutorials on how to do that and try that way. The "get over it" was really unnecessary and rude. I literally don't know how to graph with decimals,it's not me being lazy. Thanks for explaining what you have so far.
 

lex

Full Member
Joined
Mar 3, 2021
Messages
657
1. Draw the graph of y=\(\displaystyle -x^2\) and when you've done it, write \(\displaystyle \frac{ }{19}\) under every number on your y-axis.
2. Just make a table and e.g. when x=3 do (3-11), square it, then multiply by 2
3. You need to draw two separate graphs for when a>0 e.g. draw something that looks like \(\displaystyle y=x^2\), and when a<0, something like \(\displaystyle y=-x^2\).
Work out where \(\displaystyle y=a(x-h)^2\) will have its vertex and where it will cut on the y-axis and label those 2 points.
 

Chart21

New member
Joined
May 2, 2021
Messages
3
Ohhh that makes sense. When you put it that way, i get it. Thanks
 

lex

Full Member
Joined
Mar 3, 2021
Messages
657
Good luck with it.
 
Top