Answer
$$ x^2+y^2=65$$
Work Step by Step
Since the center is at the origin, we use the distance formula to find that the radius must be:
$$\sqrt{\left(-7-0\right)^2+\left(-4-0\right)^2}=\sqrt{65}$$
Thus, it follows:
$$x^2+y^2=r^2 $$
$$ x^2+y^2=65$$
