91Ó°ÊÓ

$2x+y=-3$

The above equation can be written as:

$y=-2x-3$

For each value $x$, we multiply it by $-2$and then subtract $3$to get the value of $y$.

Substitute $x=1$in $y=-2x-3$,

localid="1644817570643" role="math" $\begin{array}{rcl}y& =& -2\left(1\right)-3\\ & =& -2-3\\ & =& -5\end{array}$

It would work similarly for any value of $x$. Since each value of $x$, corresponds to only one value of $y$the equation defines a function.

For each value of $x$, square it to get the value of $y$.

$y=x^2$

Substitute $x=1$in the above equation,

localid="1644817643192" $\begin{array}{rcl}y& =& {\left(1\right)}^2\\ & =& 1\end{array}$

It would work similarly for any value of $x$. Since each value of $x$, corresponds to only one value of $y$the equation defines a function.

$x+y^2=-5$

The above equation can be written as:

$y^2=-x-5$

Substitute $x=-6$in the above equation,

localid="1644817695023" $\begin{array}{rcl}{y}^2& =& -\left(-6\right)-5\\ & =& 6-5\\ & =& 1\\ y& =& -1or1\end{array}$

It would work similarly for any value of $x$. Since each value $x$does not correspond to only one value of $y$the equation does not define a function.