Equation of a circle centred at the origin
Write the equation of a circle centred at the origin, and verify whether a given point lies inside, on, or outside the circle. Unlimited questions, five difficulty levels, and a full worked solution every time — free.
Try one
The point (-3, 4) lies on a circle centred at the origin. What is the equation of the circle?
Answer: x^2 + y^2 = 25
See one solved, step by step
A circle centred at the origin has the equation x^2 + y^2 = 49. What is its radius?
📘 Worked solution
1x2 + y2 = 49 matches x2 + y2 = r2The right side of the circle's equation is always r^2.
2r2 = 49, so r = √(49) = 7Take the square root of both sides.
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