Let α and β be the roots of equation x 2 - 6 x - 2 = 0 . If a n = α n - β n ,  …

Let α and β be the roots of equation x2-6x-2=0. If an=αn-βn,  n1, then the value of a10-2a82a9 is equal to
  1. -3
  2. 6
  3. -6
  4. 3

Solution

Given, α, β are roots of x2-6x-2=0.

⇒ α2-6α-2=0 and  β2-6β-2=0

⇒  α2-2=6α andβ2-2=6β  ...1

a10-2a82a9=α10-β10-2α8-β82α9-β9

=α10-2α8-β10-2β82α9-β9

= α 8 α 2 - 2 - β 8 β 2 - 2 2 α 9 - β 9

= α 8 6 α - β 8 6 β 2 α 9 - β 9        [  From (1)]

 =6α9-6β92α9-β9=3

Asked in: JEE Main 2015 (04 Apr)

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