Expansion using Pascal's triangle I want to expand $(3k+1)^3$. When doing this I got $27k^3+9k^2+3k+1$ but when I expanded the expression by foiling I got $27k^3+9k^2+27k+1$. Which one is correct?

You have $(3k+1)^3=(3k)^3+3(3k)^2(1)+3(3k)(1)^2+1^3$, so see what this gives when you simplify.
