Here is the diagram of a circle with its center at the origin (0,0) on a Cartesian coordinate plane. Let me know if you need any further clarification or details!

Would you like to explore more about circles? Here are some related questions:

1. What is the equation of a circle with center at the origin and radius $r$?
2. How do you find the area and circumference of a circle?
3. How do you graph a circle on a coordinate plane if you know the radius?
4. What are the differences between a circle and an ellipse in geometry?
5. How do transformations (like scaling or shifting) affect the equation of a circle?

Tip: When graphing a circle, remember that its equation is $x^2 + y^2 = r^2$, where $r$ is the radius.