§ 5

Let the numbers $x_{1}, x_{2}, x_{3}$ be pairwise distinct. Prove that for any $y_{1}, y_{2}, y_{3}$ there exists a unique polynomial of degree $\leqslant 2$, whose graph passes through the points with coordinates $\left(x_{1}, y_{1}\right),\left(x_{2}, y_{2}\right),\left(x_{3}, y_{3}\right)$.

Using the formulas for the entries of the inverse matrix, find the inverse of the matrix