f(x)=ax²+bx + cf(x+1) = a(x+1)² + b(x+1) +c = ax² + (2a+b)x + a +b+ cf(x-1) = a(x-1)² + b(x-1) + c = ax² + (b -2a)x + a -b+ cf(x+1)+f(x-1) = 2ax² + 2bx + 2(a+c) = 2x²...