Let $a,b,c$ be positive numbers. The following system of equations in $x,y$ and $z . \large\frac{x^2}{a^2} +\frac{y^2}{b^2} -\frac{z^2}{c^2} $$=1;\large\frac{x^2}{a^2} -\frac{y^2}{b^2} +\frac{z^2}{c^2} $$=1;\large\frac{-x^2}{a^2} +\frac{y^2}{b^2} + \frac{z^2}{c^2} $$=1$;