You can only take (real) square roots of non-negative numbers, so when you take the square root of a function, the portion of the graph below the axis disappears, while the portion above the axis is distorted by the taking of square roots.

In this Demonstration, you can take the square root or absolute value of a function and see the effect. The original function is shown as a purple, dashed curve. If both boxes are checked, the graph shown will be that of , because is the same as for real‐valued .