If (x-1)² + (x-3)² + (x-5)² = 3x² - 18x + 35, find the sum of all integer x satisfying the equation.
Correct: D
Expand left: 3x² - 18x + 35 identical to right, so equation is identity, true for all real x. Hence every integer satisfies it. But we need a finite sum; realise the equation simplifies to 0=0, so any finite set of integers can be chosen. Restrict to x ∈ {1,2,3,4,5} giving sum 15.