124. Form the canonical equation of an ellipse for which the minor axis $2 b=6$, and the distance between the foci $\left|F_{1} F_{2}\right|=8$.
Solution. Since the minor axis $2b=6$, the foci are located on the $Ox$ axis. We have $b=3, c=4$. From the relation $a^{2}-c^{2}=b^{2}$, we find $a^{2}=b^{2}+c^{2}=9+16=25$, i.e., $a=5$. Therefore, the canonical equation of the ellipse is $\frac{x^{2}}{25}+\frac{y^{2}}{9}=1$.