Given distinct real numbers x1, x2, ..., xn, define P(x) = (x - x1)(x - x2)...(x - xn); and for each 1 ≤ j ≤ n, define Pj(x) = P(x)/(x - xj), so that all the numbers x1, x2, ..., xn except xj are roots of Pj(x).
Problem 2. Given distinct real numbers 1, 2, ..., n, define P(x) = (x - 1)(x - 2)...(x - n); and for each 1 ≤ j ≤ n, define Pj(x) = P(x)/(x - j), so that all the numbers 1, 2, ..., n except j are roots of Pj(x).
(a) If Q(x) is any polynomial of degree less than n, prove that P(x)Q(x)/Pn(n) = Σ(j=1 to n) Q(xj)/(x - xj).
(b) Use the formula from part (a) to find a cubic polynomial Q such that Q(1) = 117, Q(2) = 239, Q(3) = 369, and Q(4) = 513. Write your answer in the standard form ar^3 + bx^2 + cx + d.