If \(U_n = kn^2 + pn\), \(U_1 = -1\), \(U_5 = 15\), find the values of k and p.
Answer Details
Un = kn2 + pn,
U1 = -1,
U5 = 15,
when n = 1 U1 = k(1)2+ p(1) = -1 k + p = -1 --------eqn1 when n = 5 U5 = k(5)2+ p(5) = 15 25k + 5p = 15 --------eqn2 multiply eqn1 by 5 and eqn2 by 1 5k + 5p = -5 -------eqn3 25k + 5p = 15 -------eqn4 eqn4 - eqn3 20k = 20 k = 1 sub for k in eqn1 1 + p = -1 p = -1 -1 = -2