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Which defines a circle?

a round figure that has no corners or vertices.

Step-by-step explanation:

A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves in a plane so that its distance from a given point is constant. The distance between any point of the circle and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.

Step-by-step explanation:

Center of a Circle

The center of a circle is the center point in a circle from which all the distances to the points on the circle are equal. This distance is called the radius of the circle.

Here, point P is the center of the circle.

center of the circle center point

Semicircle:

A semi-circle is half of a circle, formed by cutting a whole circle along a line segment passing through the center of the circle. This line segment is called the diameter of the circle.

a=24; b=12

step-by-step explanation:

a/b=2: 1

a=2b

36/(1+2)=12

b=12

a=24