Square root inequality

Algebra Level 3

True or False

n + 1 n < 1 n \large \sqrt{n + 1} - \sqrt n < \dfrac{1}{\sqrt n}

The inequality above holds for all n n such that 101 n 2000 101 \le n \le 2000 .

True False

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2 solutions

Jaydee Lucero
Jun 29, 2017

Note that ( n + 1 n ) n + 1 + n n + 1 + n = ( n + 1 ) n n + 1 + n = 1 n + 1 + n < 1 n \left(\sqrt{n+1}-\sqrt{n}\right)\cdot \frac{\sqrt{n+1}+\sqrt{n}}{\sqrt{n+1}+\sqrt{n}} = \frac{(n+1)-n}{\sqrt{n+1}+\sqrt{n}}=\frac{1}{\sqrt{n+1}+\sqrt{n}}<\frac{1}{\sqrt{n}} which is always true for all real n 1 n\geqslant1 .

nicely done !(+1)

Rishu Jaar - 3 years, 7 months ago
Me Myself
Nov 4, 2017

n + 1 n < 1 n n 2 + n n < 1 = ( n + 1 ) n = n 2 + 2 n + 1 n n 2 + n < n 2 + 2 n + 1 n 2 + n < n 2 + 2 n + 1 1 < n \sqrt{n+1}-\sqrt{n}<\frac{1}{\sqrt{n}}\\ \sqrt{n^2+n}-n<1=(n+1)-n=\sqrt{n^2+2n+1}-n\\ \sqrt{n^2+n}<\sqrt{n^2+2n+1} \\ n^2+n<n^2+2n+1\\ 1<n

And as n > 101 > 1 n>101>1 the inequality holds and the claim is false.

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