# Math Help - Composite Expression

1. ## Composite Expression

How I can tell that $4k^3+18k^2+28k+15$ is composite for an positive integer $n$?

Thanks!

2. ## Factoring

Consider that $4k^3+18k^2+28k+15=(2k+3)(2k^2+6k+5)$.

--Kevin C.

3. But where is 'n' in the expression?

I had to do a fair amount trial and error to figure out the following factorization:

$4k^3+18k^2+28k+15 = (2k+3)(2k^2 + 6k + 5)$