Question: What is the equation of a circle with center at (0, 0) and radius 4?

Options:

1. x² + y² = 16
2. x² + y² = 8
3. x² + y² = 4
4. x² + y² = 20

Correct Answer: x² + y² = 16

Solution:

The equation of a circle is (x - h)² + (y - k)² = r². Here, h = 0, k = 0, r = 4, so x² + y² = 4² = 16.