I need a help for this question please.
$P$ is a polynomial defined by $$P(x)=ab\left(a-c\right)x^{3}+\left(a^{3}-a^{2}c+2ab^{2}-b^{2}c+abc\right)x^{2}+\left(2a^{2}b+b^{2}c+a^{2}c+b^{3}-abc\right)x+ab\left(b+c\right)$$ $$ a,b,c \in \mathbb{N}$$
- I already proved that $P(x)$ is divisible by $$abx^{2}+\left(a^{2}+b^{2}\right)x+ab$$ and I found that $$P(x) = (abx^{2}+\left(a^{2}+b^{2}\right)x+ab)\left(\left(a-c\right)x+\left(b+c\right)\right)$$
2. I need help for this question. I must prove then for $$x_{0}=\left(a+b+1\right)^{n}$$ $$ n \in \mathbb{N}$$ $$P(x_{0}) \text{ is divisible by } (a+b)^3$$
thanks