Question:If`a = sqrt(6) + sqrt(5)` and` b = sqrt(6) - sqrt(5),` then `2a^2 - 5ab + 2b^2 = ?` 

A 43 
B 39 
C 31 
D 27 

+ Answer
B 

+ Explanation
`a + b = 2sqrt(6)` and ab` = (6 - 5) = 1`

`:. 2a^2 - 5ab + 2b^2`

`= 2 (a + b)^2 - 9ab`

`= 2(2sqrt(6))^2 - 9 xx 1`

`= (48 - 9) = 39`

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Irin Moni

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