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If x + y = √3 and x - y = √2, then the value of 8xy(x2 + y2) is?

A. 6

B. √6

C. 5

D. √5

Answer: Option C

Solution(By Examveda Team)

$$\eqalign{ & x + y = \sqrt 3 \,.......{\text{(i)}} \cr & x - y = \sqrt 2 \,.......(ii) \cr & {\text{From equation (i) and (ii)}} \cr & x = \frac{{\sqrt 3 + \sqrt 2 }}{2} \cr & y = \frac{{\sqrt 3 - \sqrt 2 }}{2} \cr & {\text{So, }}8xy\left( {{x^2} + {y^2}} \right) \cr & = 8 \times \frac{{\sqrt 3 + \sqrt 2 }}{2} \times \frac{{\sqrt 3 - \sqrt 2 }}{2}\left[ {\frac{{{{\left( {\sqrt 3 + \sqrt 2 } \right)}^2}}}{4} + \frac{{{{\left( {\sqrt 3 - \sqrt 2 } \right)}^2}}}{4}} \right] \cr & = 2\left( {3 - 2} \right)\left[ {\frac{{3 + 2 + 2\sqrt 6 + 3 + 2 - 2\sqrt 6 }}{4}} \right] \cr & = 2 \times 1 \times \frac{{10}}{4} \cr & = 5 \cr} $$

This Question Belongs to Arithmetic Ability >> Algebra

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Comments ( 1 )

  1. Amit Kumar
    Amit Kumar :
    3 years ago

    x + y = √3
    x – y = √2
    ∴ (x + y)2 + (x – y)2 = 3 + 2
    ⇒ 2 (x2 + y2) = 5 ...(i)
    Again,
    (x + y)2 – (x – y)2 = 3 – 2
    ⇒ 4xy = 1 ...(ii)
    ∴ (x2 + y2) = 5 × 1 = 5

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