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Question

What is the value of $\frac{4+\sqrt{2}}{\sqrt{2}+1}$?

This question was previously asked in
RRB NTPC 2019 CBT 1 Question Paper PDF (31-Jan-2021) (Shift 1)
The correct answer is
$3\sqrt{2}-2$

Simplifying the Radical Expression

The problem asks for the value of the expression $\frac{4+\sqrt{2}}{\sqrt{2}+1}$. To find the value, we need to simplify this expression, typically by rationalizing the denominator.

Rationalizing the Denominator

To rationalize the denominator $\sqrt{2}+1$, we multiply both the numerator and the denominator by its conjugate, which is $\sqrt{2}-1$.

The expression becomes:

$ \frac{4+\sqrt{2}}{\sqrt{2}+1} \times \frac{\sqrt{2}-1}{\sqrt{2}-1} $

Calculating the Numerator

Multiply the numerators:

$ (4+\sqrt{2})(\sqrt{2}-1) $

Using the distributive property (FOIL method):

$ 4(\sqrt{2}) + 4(-1) + \sqrt{2}(\sqrt{2}) + \sqrt{2}(-1) $ $ = 4\sqrt{2} - 4 + (\sqrt{2})^2 - \sqrt{2} $ $ = 4\sqrt{2} - 4 + 2 - \sqrt{2} $

Combine like terms:

$ = (4\sqrt{2} - \sqrt{2}) + (-4 + 2) $ $ = 3\sqrt{2} - 2 $

Calculating the Denominator

Multiply the denominators:

$ (\sqrt{2}+1)(\sqrt{2}-1) $

This is in the form $(a+b)(a-b) = a^2 - b^2$. Here, $a = \sqrt{2}$ and $b = 1$.

$ = (\sqrt{2})^2 - (1)^2 $ $ = 2 - 1 $ $ = 1 $

Final Simplification

Now, divide the simplified numerator by the simplified denominator:

$ \frac{3\sqrt{2} - 2}{1} $ $ = 3\sqrt{2} - 2 $

Therefore, the value of the expression $\frac{4+\sqrt{2}}{\sqrt{2}+1}$ is $3\sqrt{2}-2$. This matches Option B.

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