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The number 2+72−7\frac{\sqrt{2} + \sqrt{7}}{\sqrt{2 - \sqrt{7}}}2−7​​2​+7​​​is:
Question

The number 2+727\frac{\sqrt{2} + \sqrt{7}}{\sqrt{2 - \sqrt{7}}}​is:

A.

an irrational number

B.

a rational number

C.

an integer

D.

a natural number

Correct option is A

Given:

2+727\frac{\sqrt{2} + \sqrt{7}}{\sqrt{2 - \sqrt{7}}}

Concept Used:

An irrational number is a real number that cannot be expressed as a ratio of integers;

for example, 2\sqrt 2 is an irrational number. 

We cannot express any irrational number in the form of a ratio, such as pq\frac pq​, where p and q are integers, q≠0.

Solution:

2+727\frac{\sqrt{2} + \sqrt{7}}{\sqrt{2 - \sqrt{7}}}​​

=2+727×2727\frac{\sqrt{2} + \sqrt{7}}{\sqrt{2 - \sqrt{7}}}\times\frac{\sqrt{2 - \sqrt{7}}}{\sqrt{2 - \sqrt{7}}}

=2+7×2727×2+72+7\frac{\sqrt{2} + \sqrt{7}\times \sqrt{2 - \sqrt{7}}}{2 - \sqrt{7}} \times \frac{2 +\sqrt{7}}{2 + \sqrt{7}}

=(2+7)×27×(2+7)47\frac{(\sqrt{2} + \sqrt{7})\times \sqrt{2 - \sqrt{7}}\times (2 +\sqrt{7})}{4 - 7}

=(2+7)×27×(2+7)3\frac{(\sqrt{2} + \sqrt{7})\times \sqrt{2 - \sqrt{7}}\times (2 +\sqrt{7})}{-3}

We can say that , above expression is an irrational number.

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