Thread: 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?

Hello gwalker11

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:



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

E.g.



... and so on.

Does that make sense?

Grandad