Differential Calculus(Example 1 of the Graph of Signum Function)

Graph \[y = \frac{1}{2}(1 - {\mathop{\rm sgn}} (x)){x^2}\]

Here's what I get when I make table of values for this:

You should not be confused about the Signum Function sgn(x) because basically it only give
-1,0 and 1. Because it is a sign function, meaning it decides the sign.
If x<0,     sgn(x)=-1
   x=0       sgn(x)=0
   x>0       sgn(x)=1
Those value of sgn(x) are the range that you have to put on sgn(x) depend on the sign of
the x's.