In B 5^2 = 25. There is no x anywhere. In C f(x) = 2/x is a function of a reciprocal, not a quadratic. In D f(x) = 2x^3 + 3x^2 - 5 is a cubic. A cubic is not a quadratic. The highest power of a quadratic is x^2
That leaves A. When you expand the brackets, you get 3(x^2 + 3x- 4x - 12) 2(x^2 - x - 12) when you remove the brackets you get 2x^2 - 2x - 24. The highest power of x is x^2. This is your quadratic.
