x → 0 lim lo g ( 1 + tan x ) sin x = ?
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@Naren Bhandari Great!!!...for better understanding of others you should mention the name of method used in each case.
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Thank you !! I have added the wiki's for more info. :)
At x=0, sin(x) and tan(x) are like x, and log(1+f(x)) is like f(x). So our limit is equivalent to the limit x/x, which is 1
Relevant wiki: L'Hopital's Rule - Basic
L = x → 0 lim lo g ( 1 + tan x ) sin x = x → 0 lim 1 + tan x sec 2 x cos x = 1 A 0/0 case, L’H o ˆ pital’s rule applies. Differentiate up and down w.r.t. x .
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x → 0 lim lo g ( 1 + tan x ) sin x = x → 0 lim tan x lo g ( 1 + tan x ) tan x sin x = lim x → 0 tan x lo g ( 1 + tan x ) lim x → 0 cos x = 1
Relevant wiki : L-Hopital's Rule x → 0 lim lo g ( 1 + tan x ) sin x = x → 0 lim 1 + tan x sec 2 x cos x = x → 0 lim sec 2 x cos x ( 1 + tan x ) = 1
Relevant wiki : Taylor Series We have sin x = x − 3 ! x 3 + 5 ! x 5 − 7 ! x 7 + ⋯ & lo g ( 1 + tan x ) = tan x − 2 tan 2 x + 3 tan 3 x − 4 tan 4 x + ⋯ lo g ( 1 + tan x ) = x + 3 x 3 + 1 5 2 x 5 + ⋯ + 2 ( x + 3 x 3 + 1 5 2 x 5 + ⋯ ) 2 + Now L = x → 0 lim ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ x + 3 x 3 + 1 5 2 x 5 + ⋯ + 2 ( x + 3 x 3 + 1 5 2 x 5 + ⋯ ) 2 + ⋯ x − 3 ! x 3 + 5 ! x 5 − 7 ! x 7 + ⋯ ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ L = x → 0 lim x x ⎣ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎢ ⎡ 1 + 3 x 2 + 1 5 2 x 4 + ⋯ + 2 x ( x + 3 x 2 + 1 5 2 x 4 + ⋯ ) 2 + ⋯ 1 − 3 ! x 2 + 5 ! x 4 − 7 ! x 6 + ⋯ ⎦ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎥ ⎤ L = 1 1 = 1