If a = 1044, b = 1047, c = 1041, then

find 5(a² + b² + c² - ab - bc - ca).

135

a² + b² + c² - ab - bc - ca = \(\frac{1}{2}\) [(a - b)² + (b - c)² + (c - a)²]

                                       = \(\frac{1}{2}\) [(1044 - 1047)² + (1047 - 1041 )² + (1041 - 1044)²]

                                       = \(\frac{1}{2}\) [9 + 36 + 9] = 27

                                      = 5 × 27 = 135