How can I show that if $\nu_{n,d}:\mathbb{P}_k^n\rightarrow \mathbb{P}_k^{\binom{n+d}{d}-1}$ denotes the Veronese map, then $\nu_{n,d}(\mathbb{P}_k^n)$ is a closed irreducible variety?
I have shown that if $X^j:=X_0^{j_0}\cdots X_N^{j_N}$, where $\sum_{l=1}^Nj_l=d$, then $$\nu_{n,d}(\mathbb{P}_k^n)=V\left(\{X^iX^j-X^kX^l:i+j=k+l\}\right),$$ which implies that it is a closed variety, but how can I prove that it is irreducible?