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Ninety (90, XC) is the natural number preceded by eighty-nine and followed by ninety-one. It is the sums of the squares of the integers 2 to 6, as well as a composite number, with its divisors being 1, 2, 3, 5, 6, 9, 15, 18, 30 and 45, and its factorization is

In normal space, the interior angles of a square measure 90 degrees each. Also, in a right triangle, the angle opposing the hypotenuse measures 90 degrees, with the other two angles adding up to 90 for a total of 180 degrees.

See also: eighty, ninety, one hundred, integer, list of numbers.

Ninety is also: