Question

Let c, k ∈ R. If f(x) = (c + 1) x² + (1 - c²) x + 2k and f(x + y) = f(x) + f(y) - xy, for all x, y ∈ R, then the value of 12 (f(1) + f(2) + f(3) + ......+f (20))| is equal to _____.

Answer 1

Correct answer is 3395

Comparing equation (1) and (2)

We obtain, c = -3/2

= 2870 + 525 

= 3395