Example 2: Check whether the following are quadratic equations: (i) (x - 2)^2 + 1 = 2x - 3 (ii) x(x + 1) + 8 = (x + 2)(x - 2) (iii) x(2x + 3) = x^2 + 1 (iv) (x + 2)^3 = x^3 - 4