How are these two different general equations both represent a hyperboloid of 2 sheet? A. $\frac{x^2}{a^2}+\frac{y^2}{b^2}-z^2=k<0$
B.$\frac{x^2}{a^2}-\frac{y^2}{b^2}-\frac{z^2}{c^2}=1$
I don’t know how I can turn one into the other.
EDIT:Thanks to Bernard, I have somewhat of a clue as to where to begin. But Dividing the negative k on both both sides (assuming that the k is positive with a negative signs) and distribute the negative sign, I get $\frac{-x^2}{ka^2}-\frac{y^2}{kb^2}+\frac{z^2}{k}=1$ But this equation is still not identical with the second equation. Two of the three signs are different. 

Rewrite the first equation as 
$$\frac{z^2}{(\sqrt{-k})^2}-\frac{x^2}{(\sqrt{-k}\, a)^2}-\frac{y^2}{(\sqrt{-k}\, b)^2}=1.$$
