I have the following complex function and I would like to make it so that $g_k(z=20) = -\frac{1}{75}$ where $z+z_0=\rho \exp(j(\theta+2 k \pi))$. $$g(z)=\frac{1}{\sqrt{z+5} (z-5)}$$
I know that $z_0=-5$ as this is the point that makes the square root zero. This means that $\rho=15$ and $\theta=0$. If I put $z=20$ straight into the formula I get $\frac{1}{75}$ but I'm struggling to see how I can make this negative as the question asks. I know that I can change $k$ but seeing as $\theta=0$ and k is multiplied by $2\pi$ I think any value of k will give a positive answer. Can someone explain?