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In calculus, the trapezoidal rule (also known as the trapezoid rule or trapezium rule) [a] is a technique for numerical integration, i.e., approximating the definite integral: (). The trapezoidal rule works by approximating the region under the graph of the function f ( x ) {\displaystyle f(x)} as a trapezoid and calculating its area.
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).
Four unequal lengths, each less than the sum of the other three, are the sides of each of three non-congruent cyclic quadrilaterals, [13] which by Brahmagupta's formula all have the same area. Specifically, for sides a , b , c , and d , side a could be opposite any of side b , side c , or side d .
This property follows directly from applying the chord theorem to a third chord (a diameter) going through S and the circle's center M (see drawing). The theorem can be proven using similar triangles (via the inscribed-angle theorem ).
where θ is half the sum of any two opposite angles. (The choice of which pair of opposite angles is irrelevant: if the other two angles are taken, half their sum is 180° − θ. Since cos(180° − θ) = −cos θ, we have cos 2 (180° − θ) = cos 2 θ.) This more general formula is known as Bretschneider's formula.
The cotangents of two adjacent angles sum to 0, as do the cotangents of the other two adjacent angles. [17]: p. 26 One bimedian divides the quadrilateral into two quadrilaterals of equal areas. [17]: p. 26 Twice the length of the bimedian connecting the midpoints of two opposite sides equals the sum of the lengths of the other sides.
A formula for computing the trigonometric identities for the one-third angle exists, but it requires finding the zeroes of the cubic equation 4x 3 − 3x + d = 0, where is the value of the cosine function at the one-third angle and d is the known value of the cosine function at the full angle.
This is a special case of the n-gon interior angle sum formula: S = (n − 2) × 180° (here, n=4). [ 2 ] All non-self-crossing quadrilaterals tile the plane , by repeated rotation around the midpoints of their edges.