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Ptolemy's theorem states that the sum of the products of the lengths of opposite sides is equal to the product of the lengths of the diagonals. When those side-lengths are expressed in terms of the sin and cos values shown in the figure above, this yields the angle sum trigonometric identity for sine: sin( α + β ) = sin α cos β + cos α sin ...
The truncated cube and the truncated octahedron are Archimedean solids with 36 edges. [9] The number of domino tilings of a 4×4 checkerboard is 36. [10] Since it is possible to find sequences of 36 consecutive integers such that each inner member shares a factor with either the first or the last member, 36 is an Erdős–Woods number. [11]
Book IX, Proposition 36 of Elements proves that if the sum of the first n terms of this progression is a prime number (and thus is a Mersenne prime as mentioned above), then this sum times the n th term is a perfect number. For example, the sum of the first 5 terms of the series 1 + 2 + 4 + 8 + 16 = 31, which is a prime number. The sum 31 ...
The n th triangular number is the number of dots in the triangular arrangement with n dots on each side, and is equal to the sum of the n natural numbers from 1 to n. The sequence of triangular numbers, starting with the 0th triangular number, is
A radical ideal is an ideal that equals its own radical. In a polynomial ring k [ x 1 , … , x n ] {\displaystyle k[x_{1},\ldots ,x_{n}]} over a field k , an ideal is radical if and only if it is the set of all polynomials that are zero on an affine algebraic set (this is a consequence of Hilbert's Nullstellensatz ).
That is, if tones x, y, and z form a rising sequence of tones, then the measure of the interval from x to y plus the measure of the interval from y to z should equal the measure of the interval from x to z. Such a measure is given by the cent, which divides the octave into 1200 equal intervals (12 semitones of 100 cents each).
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In some contexts, equality is sharply distinguished from equivalence or isomorphism. [36] For example, one may distinguish fractions from rational numbers , the latter being equivalence classes of fractions: the fractions 1 / 2 {\displaystyle 1/2} and 2 / 4 {\displaystyle 2/4} are distinct as fractions (as different strings of symbols) but they ...