#### Answer

(a) This is an incomplete quadratic equation.
(b) This is not an incomplete quadratic equation.
(c) This is an incomplete quadratic equation.
(d) This is not an incomplete quadratic equation.
(e) This is an incomplete quadratic equation.
(f) This is not an incomplete quadratic equation.

#### Work Step by Step

A quadratic equation can be written in this form:
$ax^2 + bx+c = 0$
where $a,b,$ and $c$ are real numbers and $a \neq 0$
If $b=0$ or $c= 0$ (or both), then it is an incomplete quadratic equation.
(a) $x^2-4 = 0$
$a=1, b = 0, c=-4$
This is an incomplete quadratic equation.
(b) $x-4x=0$
$-3x=0$
$a=0, b = -3, c=0$
This is not a quadratic equation since $a=0$.
(c) $3x^2 = 2x$
$3x^2-2x=0$
$a=3, b = -2, c=0$
This is an incomplete quadratic equation.
(d) $2x^2-4 = 2x^2+8x$
$8x+4=0$
$a=0, b = 8, c=4$
This is not a quadratic equation since $a=0$.
(e) $x^2 = 4$
$x^2-4=0$
$a=1, b = 0, c=-4$
This is an incomplete quadratic equation.
(f) $x^2-2x-3 = 0$
$a=1, b = -2, c=-3$
This is not an incomplete quadratic equation.