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If \( \Large x = \frac{\sqrt{2}+1}{\sqrt{2}-1} \) and \( \Large x - y = 4\sqrt{2} \), then the value of \( \Large \left(x^{2} + y^{2}\right) \) is
A) 34
B) 38
C) 30
D) 32
Correct answer:
A) 34
Description for Correct answer:
\( \Large x = \frac{\sqrt{2}+1}{\sqrt{2}-1} \)
=> \( \Large x = \frac{\sqrt{2}+1}{\sqrt{2}-1} \times \frac{\sqrt{2}+1}{\sqrt{2}-1} \)
\( \Large \frac{2 + 1 + 2\sqrt{2}}{1} = 3 + 2\sqrt{2} \)
\( \Large x = 3 + 2\sqrt{2} \) ...(i)
and \( \Large x - y = 4\sqrt{2} \)
=> \( \Large y = x - 4\sqrt{2} = 3 + 2\sqrt{2} - 4\sqrt{2} \)
[Frm Eq. (i)]
\( \Large = 3 - 2\sqrt{2} \)
Now, \( \Large x^{2} + y^{2} = \left(3+2\sqrt{2}\right)^{2} + \left(3 - 2\sqrt{2}\right)^{2} \)
\( \Large = 9 + 8 + 12\sqrt{2} + 9 + 8 - 12\sqrt{2} \)
= 34
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