Question
If $f(x) = \begin{cases} \sqrt{1+kx} - \sqrt{1-kx} & \text{if } -1 \leq x \leq 0 \end{cases}$ is continuous at $x = 0$, then the value of $k$ is
If $f(x) = \begin{cases} \sqrt{1+kx} - \sqrt{1-kx} & \text{if } -1 \leq x \leq 0 \end{cases}$ is continuous at $x = 0$, then the value of $k$ is