# x and y intercepts.

• Oct 11th 2009, 02:10 PM
nautica17
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. (Headbang) 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)?
• Oct 11th 2009, 02:21 PM
Quote:

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. (Headbang) 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.
• Oct 11th 2009, 02:33 PM
Barthayn
Quote:

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. (Headbang) 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.
• Oct 11th 2009, 05:55 PM
mr fantastic
Correction in red:
Quote:

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