ANSWER
x² + y² = 9
EXPLANATION
The equation of a circle in standard form is,
[tex](x-h)^2+(y-k)^2=r^2[/tex]Where (h, k) is the center of the circle and r is the radius.
In this case, the center is (0, 0), so the equation is,
[tex]x^2+y^2=r^2[/tex]We do not know the radius of the circle, but we know that it passes through (-3, 0), so we can replace x and y with the coordinates of this point to find r,
[tex](-3)^2+0^2=r^2\text{ }\Rightarrow\text{ }r=\sqrt{(-3)^2}=3[/tex]Hence, the equation of the circle is x² + y² = 9.
