Shortcut Trick
According to fundamental geometric principles, exactly one unique circle can be drawn passing through three non-collinear points.
Any three non-collinear points form a triangle, and the center of the unique circle passing through them is the circumcenter of this triangle.
The circumcenter is geometrically determined by the intersection of the perpendicular bisectors of the sides, ensuring it is equidistant from all three vertices.
Hence, 3 non-collinear points are always required and strictly sufficient to define a single circle.
∴ The correct answer is 3.
Alternate Method
Given:
We need to determine the exact number of non-collinear points required to draw a circle.
Concept Used:
A circle is geometrically defined as the locus of all points in a plane that are at an equal distance (radius) from a fixed center point.
A
B
C
O
r
r
r
OA = OB = OC = Circumradius (r)
Calculations:
⇒ Let us assume three distinct, non-collinear points A, B, and C.
⇒ Connecting these three points visually forms a triangle ABC.
⇒ In any triangle, the perpendicular bisectors of all three sides (AB, BC, and CA) intersect perfectly at a single common point, known as the circumcenter (O).
⇒ Since point O lies on the perpendicular bisector of every side, it is exactly equidistant from all three vertices A, B, and C.
⇒ This means that the distance from O to the vertices is equal: OA = OB = OC = r (where r is the circumradius).
⇒ Because the intersection of perpendicular bisectors yields exactly one circumcenter, only one unique circle can be drawn with center O and radius r passing through A, B, and C.
⇒ If there are only 2 points, infinitely many circles can pass through them. If there are 4 or more, a single circle may not pass through all of them unless they are strictly concyclic.
⇒ Thus, a circle can always be drawn passing through exactly 3 non-collinear points.
∴ The correct answer is 3.
Additional Information
Collinear Points
Points that strictly lie on the exact same straight line are called collinear. A circle cannot be drawn passing through three collinear points because the perpendicular bisectors of the line segments formed by them are parallel and therefore never intersect to form a center.
Cyclic Quadrilateral
If a single circle successfully passes through exactly four points, those points are said to be concyclic. The quadrilateral formed by joining these points is called a cyclic quadrilateral, and its opposite interior angles will always sum up to exactly 180°.
Two Points
Infinite circles can be drawn passing through exactly two fixed points. The centers of all such possible circles will always lie anywhere on the perpendicular bisector of the line segment joining the two points.