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Measurement of tree circumference, the tape calibrated to show diameter, at breast height. The tape assumes a circular shape. The perimeter of a circle of radius R is .Given the perimeter of a non-circular object P, one can calculate its perimeter-equivalent radius by setting
where C is the circumference of a circle, d is the diameter, and r is the radius.More generally, = where L and w are, respectively, the perimeter and the width of any curve of constant width.
When calculating the length of a short north-south line at the equator, the circle that best approximates that line has a radius of (which equals the meridian's semi-latus rectum), or 6335.439 km, while the spheroid at the poles is best approximated by a sphere of radius , or 6399.594 km, a 1% difference. So long as a spherical Earth is assumed ...
Using radians, the formula for the arc length s of a circular arc of radius r and subtending a central angle of measure 𝜃 is =, and the formula for the area A of a circular sector of radius r and with central angle of measure 𝜃 is A = 1 2 θ r 2 . {\displaystyle A={\frac {1}{2}}\theta r^{2}.}
If R is a regular polygon's radius and n is the number of its sides, then its perimeter is 2 n R sin ( 180 ∘ n ) . {\displaystyle 2nR\sin \left({\frac {180^{\circ }}{n}}\right).} A splitter of a triangle is a cevian (a segment from a vertex to the opposite side) that divides the perimeter into two equal lengths, this common length being ...
The above formula can be rearranged to solve for the circumference: = =. The ratio of the circle's circumference to its radius is equivalent to 2 π {\displaystyle 2\pi } . [ a ] This is also the number of radians in one turn .
In differential geometry, the radius of curvature, R, is the reciprocal of the curvature. For a curve , it equals the radius of the circular arc which best approximates the curve at that point. For surfaces , the radius of curvature is the radius of a circle that best fits a normal section or combinations thereof.
a = the radius of the base circle h = the height of the paboloid from the base cicle's center to the edge Solid ellipsoid: a, b, c = the principal semi-axes of the ...