[latex]650=frac{2n^{^3}+3n^{2}+n}{6} Bardzo prosze krok po kroku :D Dzieki !!! 650=(2n³+3n²+n)/6

650 = [2 n³ + 3 n² + n]/6 Mnożymy obie strony równania prze 6 3 900 = 2 n³ + 3 n² + n Odgaduję, że n = 12 , bo 2 *12³ + 3*12² + 12 = 2*1728 + 3*144 + 12 = 3456 + 432 + 12 = 3 900 Odp. n = 12 ============ II sposób: 2 n³ + 3 n² + n = 3 900 n(2n² + 3n + 1) = 3 900 Δ = 9 - 4*2*1 = 9 - 8 = 1 n1 = [ -3 -1]/4 = -1 n2 = [ -3 +1]/4 = -1/2 zatem 2n² +3n +1 = 2(n +1)(n +1/2) = (n +1)(2n + 1) oraz 2 n³ + 3n² + n = n(n +1)(2n +1) n( n +1)(2n +1) = 3 900 = (2*2*3]*13*[5*5] = 12*13*25 zatem n = 12 n +1 = 13 2n +1 = 25 Odp. n = 12 =====================================================