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  2. Area of a circle - Wikipedia

    en.wikipedia.org/wiki/Area_of_a_circle

    For a polygon with 2n sides, the parallelogram will have a base of length ns, and a height h. As the number of sides increases, the length of the parallelogram base approaches half the circle circumference, and its height approaches the circle radius. In the limit, the parallelogram becomes a rectangle with width π r and height r.

  3. Parallelogram - Wikipedia

    en.wikipedia.org/wiki/Parallelogram

    The area of the parallelogram is the area of the blue region, which is the interior of the parallelogram. The base × height area formula can also be derived using the figure to the right. The area K of the parallelogram to the right (the blue area) is the total area of the rectangle less the area of the two orange triangles. The area of the ...

  4. Planimeter - Wikipedia

    en.wikipedia.org/wiki/Planimeter

    A planimeter (1908) measuring the indicated area by tracing its perimeter. Amsler polar planimeter. A linear planimeter. Wheels permit measurement of long areas without restriction. Three planimeters: digital, Prytz's (hatchet) and Amsler's (polar) Prytz planimeter with wheel at the left. The Amsler (polar) type consists of a two-bar linkage.

  5. Circle - Wikipedia

    en.wikipedia.org/wiki/Circle

    t. e. A circle is a shape consisting of all points in a plane that are at a given distance from a given point, the centre. The distance between any point of the circle and the centre is called the radius. The length of a line segment connecting two points on the circle and passing through the centre is called the diameter.

  6. List of second moments of area - Wikipedia

    en.wikipedia.org/wiki/List_of_second_moments_of_area

    I z ≈ 2 π r 3 t {\displaystyle I_ {z}\approx 2\pi r^ {3}t} . I z {\displaystyle I_ {z}} is the second polar moment of area. A filled circular sector of angle θ in radians and radius r with respect to an axis through the centroid of the sector and the center of the circle. I x = ( θ − sin ⁡ θ ) r 4 8 {\displaystyle I_ {x}=\left (\theta ...

  7. Apothem - Wikipedia

    en.wikipedia.org/wiki/Apothem

    Apothem of a hexagon Graphs of side, s; apothem, a; and area, A of regular polygons of n sides and circumradius 1, with the base, b of a rectangle with the same area. The green line shows the case n = 6. The apothem (sometimes abbreviated as apo [1]) of a regular polygon is a line segment from the center to the midpoint of one of its sides.

  8. Circumference - Wikipedia

    en.wikipedia.org/wiki/Circumference

    Circumference = π × diameter = 2 π × radius. In geometry, the circumference (from Latin circumferens, meaning "carrying around") is the perimeter of a circle or ellipse. [ 1 ] The circumference is the arc length of the circle, as if it were opened up and straightened out to a line segment. [ 2 ] More generally, the perimeter is the curve ...

  9. Ptolemy's theorem - Wikipedia

    en.wikipedia.org/wiki/Ptolemy's_theorem

    Ptolemy's theorem is a relation among these lengths in a cyclic quadrilateral. In Euclidean geometry, Ptolemy's theorem is a relation between the four sides and two diagonals of a cyclic quadrilateral (a quadrilateral whose vertices lie on a common circle). The theorem is named after the Greek astronomer and mathematician Ptolemy (Claudius ...