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Yes. Any number with a decimal representation that terminates or repeats must be a rational number. If it terminates, it's obviously rational. For example, 0.12345 is clearly 12345/100000, and the same is true for any other decimal; simply multiply it by a power of ten large enough to convert it to an integer, and then for the fraction put that integer over that power of ten.

Repeating is a little trickier; it may be best to illustrate with a couple of examples. Take the decimal 0.3333.... This multiplied by ten is 3.333...., and subtracting the original number obviously gives 3 exactly, so 10x - 1x = 9x = 3; x = 3/9 which reduces to 1/3. If it repeats in an alternating sequence (0.545454...) it's necessary to use a larger power of ten: 100x - 1x = 99x = 54; x = 54/99 = 6/11.

One or the other of these can be done for any terminating or repeating decimal expansion, therefore they must be rational.

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3.407640764076407640764076(not repeating) is rational. Rational numbers are numbers that can be written as a fraction. Irrational numbers cannot be expressed as a fraction. ---- 3.407640764076407640764076 = 3407640764076407640764076/1000000000000000000000000 Which is of the form of one_integer/another_integer so it a rational number. 3.4076... (where the 4076 repeats forever): 3.4076... = 34076/9999 = 34073/9999 Again of the form of one_integer/another_integer so it a rational number. Either way, 3.4076...4076 is a rational number. Decimal numbers that terminate, or go on forever with repeating a sequence of digits are rational. Decimal numbers that go on forever without repeating a sequence of digits are irrational, eg √2.


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