Given:
[tex]36x^2+49y^2=1764[/tex][tex]\frac{36x^2}{1764}+\frac{49y^2}{1764}=\frac{1764}{1764}[/tex][tex]\frac{x^2}{49}+\frac{y^2}{36}=1[/tex][tex]\frac{x^2}{7^2}+\frac{y^2}{6^2}=1[/tex][tex]a^2=49;b^2=36[/tex][tex]c^2=a^2-b^2[/tex][tex]c^2=49-36[/tex][tex]c^2=13[/tex][tex]c=\pm\sqrt[]{13}[/tex][tex](-\sqrt[]{13},0)\text{ \& (}\sqrt[]{13},0)\text{ are the focii of the given ellipse.}[/tex]