Prove $L_i(a_j)=\delta_{ij}$ for $1\leq i,j\leq n$ (Lagrange Interpolation)

Question

Let $V=\mathbb{R}_n[x]$ and $a_0,...,a_n$ real numbers all different. for $1\leq i\leq n$ Define $L_i \in V$ :

$L_i(x)=\prod_{j\not=i}\frac{x-a_j}{a_i-a_j} $

Prove $L_i(a_j)=\delta_{ij}$ for $1\leq i,j\leq n$

Can someone give me a hint? I will be very grateful.