The equation for any circle centered at the origin with a radius r is the following:
[tex]x^2+y^2=r^2[/tex]
By looking at the picture, we can see that the radius is 5. We can also use the distance formula to find the distance between (0,0) and (-3,-4), and we will also get 5.
Thus, r=5.
This makes the equation:
[tex]x^2+y^2=5^2[/tex]
[tex]x^2+y^2=25[/tex]
That should be your answer, let me know if this is confusing in any way.
Happy Studying~
