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In the first step both numbers were divided by 10, which is a factor common to both 120 and 90. In the second step, they were divided by 3. The final result, 4 / 3 , is an irreducible fraction because 4 and 3 have no common factors other than 1.
9 is the fourth composite number, and the first odd composite number. 9 is also a refactorable number. [2] Casting out nines is a quick way of testing the calculations of sums, differences, products, and quotients of integers in decimal, a method known as long ago as the 12th century. [3]
This helps to simplify mathematical computations by reducing the number of basic arithmetic operations needed to perform calculations. [48] The additive identity element is 0 and the additive inverse of a number is the negative of that number. For instance, + = and + =. Addition is both commutative and associative.
Because of the rules of division of signed numbers (which states in part that negative divided by positive is negative), − 1 / 2 , −1 / 2 and 1 / −2 all represent the same fraction – negative one-half. And because a negative divided by a negative produces a positive, −1 / −2 represents positive one-half.
The binary number system expresses any number as a sum of powers of 2, and denotes it as a sequence of 0 and 1, separated by a binary point, where 1 indicates a power of 2 that appears in the sum; the exponent is determined by the place of this 1: the nonnegative exponents are the rank of the 1 on the left of the point (starting from 0), and ...
45 is an odd number and a Størmer number, as well as the 9th triangular number [1] and 5th hexagonal number. [ 2 ] 45 degrees is half of a right angle. It is also the smallest positive number that can be expressed as the difference of two nonzero squares in more than two ways: 7 2 − 2 2 {\displaystyle 7^{2}-2^{2}} , 9 2 − 6 2 ...
Any two consecutive integers have opposite parity. A number (i.e., integer) expressed in the decimal numeral system is even or odd according to whether its last digit is even or odd. That is, if the last digit is 1, 3, 5, 7, or 9, then it is odd; otherwise it is even—as the last digit of any even number is 0, 2, 4, 6, or 8.
A complex number can be visually represented as a pair of numbers (a, b) forming a vector on a diagram called an Argand diagram, representing the complex plane. Re is the real axis, Im is the imaginary axis, and i is the "imaginary unit", that satisfies i 2 = −1.