Let $f$ and $g$ be two functions given by

$f=\left\{\right(0,1), (2,0), (3,-4), (4,2), (5,7\left)\right\}$ 

$g=\left\{\right(0,2),(1,0),(2,4),(-4,2),(7,0\left)\right\}$ then the range of $f\circ g$ is

Given that $f\left(x\right)=\left\{\begin{array}{cc}\sqrt{x-1}& x\ge 1\\ 4& x<1\end{array}\right.$. Find $f\left(0\right)$.

Given that $f\left(x\right)=\left\{\begin{array}{cc}\sqrt{x-1}& x\ge 1\\ 4& x<1\end{array}\right.$. If $f\left(3\right)=\sqrt{k}$, then $k$ is

Given that $f\left(x\right)=\left\{\begin{array}{cc}\sqrt{x-1}& x\ge 1\\ 4& x<1\end{array}\right.$. If $f(a+1)=\sqrt{k}$ the find the value of $k$. $($Given that $a\ge 0)$.