Answer
a) f is not a function from R to R, because for x = 0, we would have $f(0) = 1/0 $ which is undefined.
b) f is not a function from R to R, because for every x <0, we would have a negative number under the square roots. For example $f(-1) = \sqrt(-1)$ which is not a real number (Domain is R) but a complex(imaginary number).
c) f is not a function from R to R, because there are 2 values assigned to every x. So f is not a function.
Work Step by Step
The explanation are included in the answers above already.
