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Show that there is no positive integer n for which √n-1 + √n+ 1 is rational?
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Proof that there is no positive integer n for which √n-1 √n 1 is rational


Assumption

We assume that there exists a positive integer n such that √n-1 √n 1 is rational.

Deriving a Contradiction

Let's simplify the expression by multiplying ( √n-1 + 1) with (√n-1 - 1):

(√n-1 + 1) (√n-1 - 1) = (√n-1)² - 1

= n - 2√n + 1 - 1

= n - 2√n

We know that √n is irrational if n is not a perfect square. So, if √n is irrational, then n - 2√n is also irrational.

If √n is rational, then we can express it as a fraction p/q, where p and q are coprime integers. Substituting this value in n - 2√n, we get:

n - 2√n = n - 2(p/q) = (nq - 2p)/q

Since p and q are coprime, nq - 2p and q are also coprime. Hence, n - 2√n is irrational.

Thus, we have derived a contradiction. Hence, our assumption that there exists a positive integer n such that √n-1 √n 1 is rational is false.

Conclusion

Therefore, there is no positive integer n for which √n-1 √n 1 is rational.
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Show that there is no positive integer n for which √n-1 + √n+ 1 is rational?
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