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What sets are closed under division?
For example:* The set of real numbers, excluding zero * The set of rational numbers, excluding zero * The set of complex numbers, excluding zero You can also come up with other sets, for example: * The set {1} * The set of all powers of 2, with an integer exponent, so {... 1/8, 1/4, 1/2, 1, 2, 4, 8, 16, ...}
True or False The set of whole numbers is closed under subtraction Why?
False. The set of whole numbers is not closed under subtraction. Closure under subtraction means that when you subtract two whole numbers, the result is also a whole number. However, this is not always the case with whole numbers. For example, subtracting 5 from 3 results in -2, which is not a whole number.
Are the set of positive fractions closed under division?
Yes, because for any x and y that are positive fractions (y not equal to zero), x/y is also a positive fraction. Note that whole numbers are considered fractions with denominators of 1 -- otherwise it doesn't work.
Which of the following is an example of why irrational numbers are not closed under addition?
Don't know about the "following" but any irrational added to its additive inverse is 0, which is rational. Therefore, the set of irrationals is not closed under addition.
Is irrational numbers closed under division?
Nope. Quick example: e (2.71828) is irrational. Therefore 2*e is irrational making both of them elements of the set of irrational numbers. However, dividing the two, e/(2*e), gives you 1/2, which is a rational number.
