1. The problem is to solve various problems related to circles (circulus). 2. The main formulas used in circle problems include: - Circumference: $$C = 2\pi r$$ where $r$ is the radius. - Area: $$A = \pi r^2$$ - Equation of a circle centered at $(h,k)$: $$(x - h)^2 + (y - k)^2 = r^2$$ 3. Important rules: - The radius is the distance from the center to any point on the circle. - The diameter is twice the radius. - The circumference is the perimeter of the circle. 4. Example problem: Find the circumference and area of a circle with radius 5. 5. Solution: - Circumference: $$C = 2\pi \times 5 = 10\pi$$ - Area: $$A = \pi \times 5^2 = 25\pi$$ 6. Another example: Find the equation of a circle with center at $(3,-2)$ and radius 4. 7. Solution: - Equation: $$(x - 3)^2 + (y + 2)^2 = 4^2 = 16$$ 8. These formulas and steps can be applied to solve any circle-related problem by identifying the radius, center, or points on the circle.