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The equation of a circle with centre at the origin and radius 5 is:
Ax² + y² = 25
Bx² + y² = 5
Cx² + y² + 25 = 0
Dx² − y² = 25
Answer & Solution
Correct answer: A. x² + y² = 25
1. For a circle centred at the origin and radius r, any point (x, y) on it has distance r from O.
2. So x² + y² = r².
3. With r = 5: x² + y² = 25.
4. So the equation is x² + y² = 25.
5. The other forms do not match the standard centred-at-origin equation.
_Source: SCERT Kerala Std X Mathematics Part-2, Chapter 9-11 (pp 227-246, 2019 ed.)._
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