Summer Fruit Four whole or irrational Statement
The idea is that there can be equal to a proper fraction, ie it is not a regular number.
To demonstrate this statement, we will support the demonstration of the irrationality of √ 2, which normally must all have seen in class.
In case you have not seen I do a quick check. We proceed by contradiction, assume that the value of this number is a fraction a / b, a and b coprime, because if they were not, simplify the fraction. After taking equality and denominator roots are removed and the expression is reached 2b 2 = a 2 , so that 2 is even. Because of that, a must be even, as if it were odd, 2 should also be odd. Then a = 2k for some k, and substituting in the previous equality, we come to 2b 2 = 4k 2, so 2 b 2 = 2k, where we also b is even, which is absurd, since we had assumed that the fraction a / b could not be further simplified. Hence, √ 2 can not be rational.
applied to the problem at hand, we can start proving that for all natural n, √ n must be either integer or irrational. As
proceed by reductio ad absurdum. If not an integer or irrational, √ \u200b\u200bn is of the form a / b, and we can simplify the fraction to a and b are relatively prime. Also, b must be greater than 1, because if not, √ n would be over.
Now suppose that p is a prime that divides n (n = pk). If we remove the root squaring and denominators we arrive at the following equation with integers, nb = PKB 2 2 = a 2 , then p divides 2 aa, and therefore must divide a. That means that a = pt, and the equality becomes PKB 2 = p t 2 2 . Simplifying kb 2 = pt 2 . As p does not divide ab, he was a cousin, you must divide k, so k = ps, so 2 sb = t 2 , and we can repeat reasoning. That means that all prime factors of p are repeated twice, which means that its root is full. Which was discarded from the outset.
can also be reasonable to assume that we have found the smallest n for which this expression is given, and the method we have built, you come to another value s less than n is of this form.
Once seen, we can build another similar reasoning to cube roots, as the method to remove a cube root is simply to raise the bucket, and would get another expression of the form nb 3 = PKB 3 = to 3 and reasoner in the same way. In fact, it can be shown for roots of generic index.
Now imagine that we have natural nym. If the expression √ n + √ m 3 = a / b, a and b mutually prime and b> 1, then √ n can not be whole because we could clear 3 √ m in the form of an irreducible fraction, we know that is impossible. Nor 3 √ m can be whole for the same reason, ie, we could clear √ n would be a fraction. However, equality √ n + √ 3 m = a / b we can remove and clear denominators, leaving b * 3 √ m = a - b √ n. Raise the bucket to remove the cube root, and get 3 mb = a 3 - 3rd 2 √ n + b 3anb 2 - 3 nb * √ n (this can be checked if we develop cube subtraction, multiplying a polynomial or three times a - b √ n and applying properties of the square root). Grouping
roots, we have the expression 3 mb = a + 3anb 3 2 - (3a 2 b + nb 3) √ n, so we can solve for √ n, becoming equal to 3 + 3anb 2 - 3 mb = (3a 2 b + nb 3) √ √ n and thus n = (a + 3anb 3 2 - 3 mb) / (the 3rd 2 b + nb 3). Thus, √ n should be rational or integer, which can not by reasoning that we have done before. Then the sum
√ n + √ m 3 is either an integer, or is an irrational number, we wanted to prove.