When you square it you have,
Of radius 2.
But the original function,
Is a semi-circle because we only take the positive side of the circle (since square root only returns positive values).
Since the radius it 2 it starts at zero and goes all the way until 2.
The curve cannot be a function. Because for example, lie on this curve. Thus, for an absicca (x) values we have two ordinate (y) values which means it cannot be a function.Why is not a function and is?
The other curve only has one value.
Because when you have the only solution (real) for y is .
While in the first curve there are two solutions for y, (because it has even degree).