[HOMEWORK, help and explanation will be more appreciated than the solution]
Hi I need some help proving that a general polynomial $\sum_{ i=0 }^{ k }{ { b }_{ i }{ n }^{ i }}=\Omega(n^{k})$ while some of the coefficients might be negative, in exception of $b_{k}>0$. I was thinking that as in the general case I could do the following $c\cdot(n^{k})\le|\sum_{ i=0 }^{ k }{ { b }_{ i }{ n }^{ i }}|=\sum_{ i=0 }^{ k }{ { b }_{ i }{ n }^{ i }}\le\sum_{ i=0 }^{ k }{ |{ b }_{ i }|\cdot|{ n }^{ i }|}$ but now I'm stuck and I don't know how to go on...