15. Determine the equation of the line

In an isosceles $\triangle ABC$, $AB = AC$. The base $BC$ lies on the $x$-axis, $A$ lies on the $y$-axis, and $x+9y+18=0$ is the equation of $AB$. Find the equation of the straight line along with $AC$.

 

Answer:

 

The equation of the straight line along $AC$ is