Returns the polynomial that exactly interpolates the given values.
InterpolatingPolynomial[{f1, f2, …}, x]
InterpolatingPolynomial[{{x1, f1}, {x2, f2}, …}, x]
InterpolatingPolynomial[{{{x1, y1, …}, f1}, {{x2, y2, …}, f2}, …}, {x, y, …}]
InterpolatingPolynomial[{{{x1, …}, f1, df1, …}, …}, {x, …}]
InterpolatingPolynomial[{1, 4, 9}, x]
→ 1 + (-1 + x)*(1 + x)