# Simple Graphing Question

• Apr 19th 2009, 07:48 PM
gwalker11
Simple Graphing Question
Ok, this is going to sound stupid... because I am majoring in math... and have been graphing simple graphs for years...... but I was just tutoring a kid.. and was trying to figure out a quadratic equation from looking at the graph.... and I have a complete brain fade.

So.... if the equation is y = (1/4)x^2
I thought.... you would make a table multiply by the reciprocal..

*4 | x | y|
-8 | -2|4
-4| -1| 1
0 |0 |0
4 |1 |1
8 | 2 |4
12|3 |9

but to do it the other way... clearly when x=2.. y = (1/4)x^2 = 2*2*0.25 = 1
.... but in the way high school tells you to do horizontal stretch... why is it saying when x is 4, y is 1?
What am I missing?
• Apr 19th 2009, 11:16 PM
Hello gwalker11
Quote:

Originally Posted by gwalker11
Ok, this is going to sound stupid... because I am majoring in math... and have been graphing simple graphs for years...... but I was just tutoring a kid.. and was trying to figure out a quadratic equation from looking at the graph.... and I have a complete brain fade.

So.... if the equation is y = (1/4)x^2
I thought.... you would make a table multiply by the reciprocal..

*4 | x | y|
-8 | -2|4
-4| -1| 1
0 |0 |0
4 |1 |1
8 | 2 |4
12|3 |9

but to do it the other way... clearly when x=2.. y = (1/4)x^2 = 2*2*0.25 = 1
.... but in the way high school tells you to do horizontal stretch... why is it saying when x is 4, y is 1?
What am I missing?

I'm not at all sure why you would want to multiply by the reciprocal. This is a method that I have never seen! But if you do it this way, you must first re-write the equation as:

$y=(\tfrac{1}{2}x)^2$

So you'll need to multiply by $2$, not $4$. Then start with multiples of $2$:

E.g.
$(-4)\text{ = value of }x \rightarrow (-2) \rightarrow 4 = \text{ value of }y$

$(-2)\text{ = value of }x\rightarrow (-1) \rightarrow 1 = \text{ value of }y$

... and so on.

Does that make sense?