# Thread: x and y intercepts.

1. ## x and y intercepts.

I need to find the x and y intercepts of this:

f(x) = x^3 - 4x

The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?

2. Originally Posted by nautica17
I need to find the x and y intercepts of this:

f(x) = x^3 - 4x

The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?
The y-intercept is given by f(0), so the y-intercept is zero. The x intercept is occurs when $\displaystyle y=0=x^3-4x$, so just solve this equation.

3. Originally Posted by nautica17
I need to find the x and y intercepts of this:

f(x) = x^3 - 4x

The y-intercept is just zero right? So how about the x's? I haven't done this in a while. Do you just factor this or do you do something else? I know it's easy.. but I'm having a major brain fade here. I'm guessing the x is on -4 and 4?

Edit: I think I got it. x-intercepts are on (-2,0) and (2,0)?
The x-intercepts are (x-2)(x+2) and 0.

4. Correction in red:
Originally Posted by Barthayn
The x-intercepts are the solutions to (x-2)(x+2)=0 and x = 0.