Quantitative Aptitude Ques 1592

Question: If $ x=\frac{\sqrt{2}+1}{\sqrt{2}-1} $ and $ x-y=4\sqrt{2}, $ then the value of $ (x^{2}+y^{2}) $ is

Options:

A) 34

B) 38

C) 30

D) 32

Show Answer

Answer:

Correct Answer: A

Solution:

  • $ x=\frac{\sqrt{2}-1}{\sqrt{2}-1} $
    $ \Rightarrow $ $ x=\frac{\sqrt{2}+1}{\sqrt{2}-1}\times \frac{\sqrt{2}+1}{\sqrt{2}+1} $

$ \Rightarrow $ $ x=\frac{2+1+2\sqrt{2}}{1} $

$ \Rightarrow $ $ x=3+2\sqrt{2} $ … (i) and $ x-y=4\sqrt{2} $

$ \Rightarrow $ $ y=x-4\sqrt{2} $ $ =3+2\sqrt{2}-4\sqrt{2} $ [from Eq. (i)] $ =3-2\sqrt{2} $ Now, $ x^{2}+y={{(3+2\sqrt{2})}^{2}}+{{(3-2\sqrt{2})}^{2}} $ $ =9+8+12\sqrt{2}+9+8-12\sqrt{2}=34 $