# Composite Expression

• December 23rd 2008, 05:51 AM
Winding Function
Composite Expression
How I can tell that $4k^3+18k^2+28k+15$ is composite for an positive integer $n$?

Thanks!
• December 23rd 2008, 06:58 AM
TwistedOne151
Factoring
Consider that $4k^3+18k^2+28k+15=(2k+3)(2k^2+6k+5)$.

--Kevin C.
• December 23rd 2008, 06:58 AM
Isomorphism
But where is 'n' in the expression? (Evilgrin)

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

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