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Graph Parabolas — easy as 1-4-9

Example: Graph $y=2x^2-4x-8$

$a = 2, b = -4, c = -8$

The vertex is

$x=\frac{-b}{2a}$

$=\frac{-(-4)}{2(2)}$
$=\frac{4}{4}$
$=1$

Okay, the vertex is at (1, ?).
How do I find the y-coordinate?

Plug in x.

$y=2(1)^2-4(1)-8$

$=2-4-8$
$=-10$

So, the vertex is at (1, -10).

Now here's a trick you won't find in your math book.

You can graph the rest of the function in less than a minute, using the 1-4-9 method. Here's how:

From the vertex, move
right 1, move up 1a.

From the vertex, move
right 2, move up 4a.

From the vertex, move
right 3, move up 9a.

Reflect points to the left, & graph parabola.

You can use the 1-4-9 method to graph any quadratic equation. It's fast, it's easy, and it works every time!

Courtesy of Michael Lipsky, experienced teacher and tutor.
In-Person, one-on-one.

(954) 560-1646