We determine a polynomial p for given support points \((x_i,y_i)\) with \(p(x_i) = y_i\) . We find this polynomial by evaluating the Lagrange interpolation formula. As simple as it is to determine this interpolation polynomial, so effective is this tool: We will apply this polynomial interpolation in later chapters several times, for example for the numerical approximation of certain integrals or solutions of initial value problems.