Question: What is the equation of a circle with center at (0, 0) and radius 5?

Options:

1. x² + y² = 25
2. x² + y² = 5
3. x² + y² = 10
4. x² + y² = 20

Correct Answer: x² + y² = 25

Solution:

The equation of a circle is (x - h)² + (y - k)² = r². Here, h=0, k=0, r=5, so x² + y² = 5² = 25.