If f(x) = ax^2 + bx + c, and f(1) = 6, f(2) = 15, and f(3) = 28, what is the value of a + b + c?
Correct: D
Since f(1) = a + b + c, we just need to find f(1). We are given that f(1) = 6. Therefore, a + b + c = 6. Alternatively, we can set up a system of equations: a + b + c = 6, 4a + 2b + c = 15, 9a + 3b + c = 28. Solving this system, we find a = 2, b = 1, c = 3. Thus, a + b + c = 2 + 1 + 3 = 6.