Answer
when $k<0$, the vertex of the parabola lies below the $x-$axis.
When $k>0$, the vertex of the parabola lies above the $x-$axis.
Work Step by Step
For the parabola equation $y=x^2+k$ ; The vertex lies at the point$(0,k)$. If $k$ is a positive number, the parabola is shifted $k$ units upward and, if $k$ is a negative number, the parabola is shifted $k$ units downward.
