Q.If ???? = 3 + 2 and ???? = 3 − 2 , then what is the value of 8 ???? ???? ( ???? 2 + ???? 2 ) ? (a) 24 (b) 80 (c) 16 (d) 8
Answer: B
\(x + y = \sqrt{3} + \sqrt{2} + \sqrt{3} - \sqrt{2} = 2\sqrt{3}\) \(xy = (\sqrt{3} + \sqrt{2})(\sqrt{3} - \sqrt{2}) = 3 - 2 = 1\) \(\therefore\ 8xy(x^2 + y^2)\) \(= 8xy[(x + y)^2 - 2xy]\) \(= 8 \times 1 \times [(2\sqrt{3})^2 - 2 \times 1]\) \(= 8[12 - 2] = 8 \times 10 = 80\)
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