How to graph y=x^2+2x-15?

Question

I have completely forgotten how to do this and I have been searching for a long time and can't figure out how to solve this.

Answer 1

That is a quadratic equation. It'll look like an arch when graphed.

First find it's x-intercepts. This factors into (x+5)(x-3)

Therefore, it's x-intercepts are -5, and 3

Then, find it's vertex (the minimum or the maximum)

It's -b/2a, so -2 / 2(1) = -1.

Or you can make a table of values.

Answer 2

I would say use a graphing calculator but I'm guessing you don't have one.  All I remember is the slope-intercept form y=mx+b. So the curve will be some kind of parabola hitting the y axis at -15. Sorry that wasn't really too much help. Or factoring? remember the phrase FOIL? first outer inner last?

Answer 3

I don't know if there is any quick and easy way to do this.

I would start out by finding the x and y intercepts. You can do this by substituting x and then y to 0. For, example x=0, => y=-15.

Keep plotting points on the curve until you figure out. It will be a U shaped (parabola) of some sort. Thats the best way. Make sure you get the intercepts correct, and a few other points and the curve should look good enough.

Of course, you can always check your answers on a graphing calculator.

Try some of these links out:

http://www.purplemath.com/modules/grphqu...

http://www.intmath.com/Quadratic-equatio...