why is it that when i type in $\displaystyle y=\sqrt{1-x^2}$ i do not get a unit circle as a result?
is that not the equation for a unit circle in terms of x?
That is only the top half of the circle (Remember a circle isn't a function)
$\displaystyle x^2+y^2=1 \iff y^2=1-x^2 \implies y=\pm\sqrt{1-x^2}$
The bottom half has the negative from the plus or minus.
If your calculator does parametric graphs you could graph the circle with
$\displaystyle x(t)=\cos(t),y(t)=\sin(t), t \in [0 ,2\pi]$