Question

If lim x 0 3 + α sin x + β cos x + log e ( 1 x ) 3 tan 2 x = 1 3 , then 2α − β is equal to

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Answer :

lim x 0 3 + α sin x + β cos x + log e ( 1 x ) 3 tan 2 x = 1 3

lim x 0 3 + α [ x x 3 3 ! + ] + β [ 1 x 2 2 ! + x 4 4 ! ] + ( x x 2 2 x 3 3 ) 3 tan 2 x = 1 3

lim x 0 ( 3 + β ) + ( α 1 ) x + ( 1 2 β 2 ) x 2 + 3 x 2 × x 2 tan 2 x = 1 3

β + 3 = 0 , α 1 = 0  and  1 2 β 2 3 = 1 3

β = 3 , α = 1

2 α β = 2 + 3 = 5

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