The equation for any circle centered at the origin with a radius r is the following:
![x^2+y^2=r^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/evvua4reaxtgq9ad51rvqst7lgv23kk3oq.png)
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:
![x^2+y^2=5^2](https://img.qammunity.org/2020/formulas/mathematics/high-school/6pob71qfn62yi3tjaf8xcsm6n1r2ti9ry4.png)
![x^2+y^2=25](https://img.qammunity.org/2020/formulas/mathematics/high-school/r3g3yjuafli8ld5r046p68wd6049xsijrz.png)
That should be your answer, let me know if this is confusing in any way.
Happy Studying~