Consider the arbitrary linear equation \[ ax + b = 0 \] for real numbers $a$, $b$ with $a\neq0$. Rearranging, it follows that \[ b = -ax , \] and $a$ has an inverse since it is a nonzero field element, so this has the solution \[ x = -b/a . \]

Consider the arbitrary linear equation \[ ax + b = 0 \] for real numbers $a$, $b$ with $a\neq0$. Rearranging, it follows that \[ b = -ax , \] and $a$ has an inverse since it is a nonzero field element, so this has the solution \[ x = -b/a . \]