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
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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