Which of the following is a quadratic equation? Choose the correct choice: A) x1/2 + 2x + 3 = 0 B) x - 1)(x + 4) = x2 + 1 C) x4 - 3x + 5 = 0 D) (2x + 1)(3x - 4) = 2x2 + 3 E) None of these
Sol.(d) Equations in options (a) and (c) are not quadratic equations as in (a) max. power of x is fractional and in (c), it is not 2 in any of the terms.   For option (b), (x – 1)(x +4) = x2 + 1   or x2 + 4x - x + 4 = x2 + 1   or 3x - 5 = 0   which is not a quadratic equations but a linear.   For option (d), (2x + 1)(3x – 4) = 2x2 + 3   or 6x2 - 8x + 3x - 4 = 2x2 + 3   or 4x2 - 5x - 7 = 0   which is clearly a quadratic equation.   Answer (2x + 1)(3x - 4) = 2x2 + 3
<result>D</result>
Which of the following is a quadratic equation?