1. Synthetic substitution regarding cubic

I really need help on this!
It's for Honors Algebra II.

I need to solve for k.
The problem is x^3+8x^2+Kx+21; x-6
The x-6 is the thing that goes in the box, if you know what I'm tAlking about.
If you could help me, I would really appreciate it.
Thanks![HTML][/HTML]

2. Originally Posted by VictoriaMarie
I really need help on this!
It's for Honors Algebra II.

I need to solve for k.
The problem is x^3+8x^2+Kx+21; x-6
The x-6 is the thing that goes in the box, if you know what I'm tAlking about.
If you could help me, I would really appreciate it.
Thanks!
I would help you solve it, except $x^3+8x^2+Kx+21$ is not an equation. What exactly do you use $x-6$ for?

3. Sorry.
Here's a site that pretty much explains what I'm learning.
Synthetic Division -- from Wolfram MathWorld
This I understand, but i have no clue how to solve for that k.

4. you are looking for the value of k such that (x-6) is a factor of the given cubic.

Code:
6]    1        8         k          21

6        84       6(k+84)
----------------------------------------
1       14      k+84     21+6(k+84)
for (x-6) to be a factor, the remainder, 21 + 6(k+84), has to equal 0.