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  2. Circumference - Wikipedia

    en.wikipedia.org/wiki/Circumference

    The term circumference is used when measuring physical objects, as well as when considering abstract geometric forms. When a circle's diameter is 1, its circumference is . When a circle's radius is 1—called a unit circle—its circumference is .

  3. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    The ratio of a circle's circumference to its diameter is π (pi), an irrational constant approximately equal to 3.141592654. The ratio of a circle's circumference to its radius is 2 π . [ a ] Thus the circumference C is related to the radius r and diameter d by: C = 2 π r = π d . {\displaystyle C=2\pi r=\pi d.}

  4. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    Let A′ be the point opposite A on the circle, so that A′A is a diameter, and A′AB is an inscribed triangle on a diameter. By Thales' theorem, this is a right triangle with right angle at B. Let the length of A′B be c n, which we call the complement of s n; thus c n 2 +s n 2 = (2r) 2. Let C bisect the arc from A to B, and let C′ be the ...

  5. Measurement of a Circle - Wikipedia

    en.wikipedia.org/wiki/Measurement_of_a_Circle

    Proposition one states: The area of any circle is equal to a right-angled triangle in which one of the sides about the right angle is equal to the radius, and the other to the circumference of the circle. Any circle with a circumference c and a radius r is equal in area with a right triangle with the two legs being c and r.

  6. French catheter scale - Wikipedia

    en.wikipedia.org/wiki/French_catheter_scale

    The French scale measures and is proportional to the outer diameter of a catheter, with 1 French ... Circumference (mm) Outer diameter (mm) (inches) 2 2.1 0.67 0.026 ...

  7. Perimeter - Wikipedia

    en.wikipedia.org/wiki/Perimeter

    If the diameter of a circle is 1, its circumference equals π Main article: Circumference The perimeter of a circle , often called the circumference, is proportional to its diameter and its radius .

  8. Diameter - Wikipedia

    en.wikipedia.org/wiki/Diameter

    In this context, a diameter is any chord which passes through the conic's centre. A diameter of an ellipse is any line passing through the centre of the ellipse. [7] Half of any such diameter may be called a semidiameter, although this term is most often a synonym for the radius of a circle or sphere. [8] The longest diameter is called the ...

  9. Unit circle - Wikipedia

    en.wikipedia.org/wiki/Unit_circle

    In mathematics, a unit circle is a circle of unit radius—that is, a radius of 1. [1] Frequently, especially in trigonometry, the unit circle is the circle of radius 1 centered at the origin (0, 0) in the Cartesian coordinate system in the Euclidean plane. In topology, it is often denoted as S 1 because it is a one-dimensional unit n-sphere ...