WBBSEClass XMathematicsQuadratic Surds03 Mark2024 Moderate

QQuestion

If x = √3 + √2 and y = 1/x then find (x + \frac{1}{\text{x}})² + (\frac{1}{\text{y}} – y)²

Exam-ready answer 03 Mark

Answer

x = √3 + √2

\frac{1}{\text{x}} = \frac{1}{\text{√3 + √2}}

= \frac{1}{\text{√3 + √2}} × \frac{√3 - √2}{\text{√3 - √2}}

= \frac{√3 - √2}{\text{(√3)² - (√2)²}}

\frac{1}{\text{x}}  = √3 – √2

Also, y = \frac{1}{\text{x}} = √3 – √2 and \frac{1}{\text{y}} = x = √3 + √2

Now, (x + \frac{1}{\text{x}})² + (\frac{1}{\text{y}} – y)² = {(√3 + √2) + (√3 – √2)}² + {(√3 + √2) – (√3 – √2)}²

= (2√3)² + (2√2)²

= 12 + 8

= 20

∴ (x + \frac{1}{\text{x}})² + (\frac{1}{\text{y}} – y)² = 20

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