Answer
$\frac{x^2}{81}+\frac{y^2}{9}=1$
Work Step by Step
Major axis is horizontal.
$(±9,0)=(±a,0)$
$a=9$
$2b=6$
$b=3$
Standard form when major axis is horizontal:
$\frac{x^2}{a^2}+\frac{y^2}{b^2}=1$
$\frac{x^2}{9^2}+\frac{y^2}{3^2}=1$
$\frac{x^2}{81}+\frac{y^2}{9}=1$
