# Thread: Find all the zeros of the function algebraically.

1. ## Find all the zeros of the function algebraically.

Find all real zeros of the function algebraically.

f(x)= x^4 - x^3 - 15x^2

help anyone?

2. ## Re: Find all the zeros of the function algebraically.

$x^4-x^3-15x^2=x^2(x^2-x-15)$
Can you find all the zeros in that?

3. ## Re: Find all the zeros of the function algebraically.

Originally Posted by Shakarri
$x^4-x^3-15x^2=x^2(x^2-x-15)$
Can you find all the zeros in that?
no i can not =/

can you help me, i'm getting desperate.

4. ## Re: Find all the zeros of the function algebraically.

0,0, $1\pm\sqrt{61}/2$

5. ## Re: Find all the zeros of the function algebraically.

Originally Posted by sciencepal
0,0, $1\pm\sqrt{61}/2$
can you please show how you got that? this is just a sample problem and i'm goin to have a similar problem on my test, i'd appreciate it.

6. ## Re: Find all the zeros of the function algebraically.

Shakarri meant that one, $x^2(x^2-x-15)$

now you have in the brackets a second degree equation, it's impossible that you can not find the zeros from that one, try it,

ps: oops, we might have answered in the same time

7. ## Re: Find all the zeros of the function algebraically.

Originally Posted by dokrbb
Shakarri meant that one, $x^2(x^2-x-15)$

now you have in the brackets a second degree equation, it's impossible that you can not find the zeros from that one, try it,

dokrbb
so you factored out an x squared, i see that, but i still don't know how to find the zeros from that one. =/

8. ## Re: Find all the zeros of the function algebraically.

$x^2(x^2-x-15)$ is zero when either $x^2=0$ or $x^2-x-15=0$
Find the values of x which make either of those zero.

9. ## Re: Find all the zeros of the function algebraically.

Originally Posted by Shakarri
$x^2(x^2-x-15)$ is zero when either $x^2=0$ or $x^2-x-15=0$
Find the values of x which make either of those zero.
that sounds completely foreign to me =/

there is a similar problem to this on my test, and i'm trying to figure this out. i was hoping you or someone would briefly post the steps used to solve it. sorry if i sound rude

10. ## Re: Find all the zeros of the function algebraically.

Never mind i got it.