The problem asks us to identify which of the given equations are quadratic equations in $x$. A quadratic equation in $x$ has the general form $ax^2 + bx + c = 0$, where $a$, $b$, and $c$ are constants and $a \ne 0$.

1. Problem Description

The problem asks us to identify which of the given equations are quadratic equations in $x$. A quadratic equation in $x$ has the general form $ax^2 + bx + c = 0$, where $a$, $b$, and $c$ are constants and $a \ne 0$.

2. Solution Steps

a) The equation is $x^2 + 3 = 0$. This can be written as $1x^2 + 0x + 3 = 0$. Here $a=1$, $b=0$, $c=3$. Since $a \ne 0$, this is a quadratic equation.

b) The equation is $-x^2 + 2x = 7$. This can be rewritten as $-x^2 + 2x - 7 = 0$. Here $a=-1$, $b=2$, $c=-7$. Since $a \ne 0$, this is a quadratic equation.

c) The equation is $3x - 4y = 2$. This is a linear equation in two variables, $x$ and $y$. It does not contain an $x^2$ term, so it is not a quadratic equation in $x$.

d) The equation is $2 - 3x + 0x = 0$. This simplifies to $2 - 3x = 0$, or $-3x + 2 = 0$. This is a linear equation in $x$. It does not contain an $x^2$ term, so it is not a quadratic equation in $x$.

3. Final Answer

a, b