L = x → 0 lim ( e ( 1 + x ) 1 / x ) sin x 1
If L = e k , where k is a real number , find the value of k .
Clarification : e denotes Euler's number , e ≈ 2 . 7 1 8 2 8 .
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Good...thanks sir
In this solution, l o g refers to the natural logarithm.
L = x → 0 lim ( e ( 1 + x ) x 1 ) sin x 1 lo g ( L ) = x → 0 lim ⎝ ⎜ ⎜ ⎛ sin x lo g ( e ( 1 + x ) x 1 ) ⎠ ⎟ ⎟ ⎞ = x → 0 lim ( sin x x lo g ( 1 + x ) − lo g e ) = x → 0 lim ( x sin x lo g ( 1 + x ) − x ) Use L’Hopital’s Rule as 0 0 = x → 0 lim ( sin x + x cos x 1 + x 1 − 1 ) Use L’Hopital’s Rule again as 0 0 = x → 0 lim ( 2 cos x − x sin x − ( 1 + x ) 2 1 ) = − 2 1 lo g ( L ) = − 2 1 ⟹ L = e − 2 1 ⟹ k = − 2 1
Simple standard approach.
In such cases, I find that it's often most helpful to consider the Maclaurin expansion directly, since it's not clear how many applications of L'hopital are necessary.
@Sam Bealing , you should have noted that l o g pertains to the natural logarithm l n because we have a different way of getting the derivatives of those with the form lo g b ( x ) .
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I have corrected that.
For calculus questions, lo g almost always refers to in base e .
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It is nice to learn something new (for me). Thank you, @Calvin Lin .
I did it by exact same method.
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L = x → 0 lim ( e ( 1 + x ) x 1 ) sin x 1 = x → 0 lim exp ( sin x 1 ( x 1 ln ( 1 + x ) − 1 ) ) = x → 0 lim exp ( sin x 1 ( x 1 ( x − 2 x 2 + 3 x 3 − . . . ) − 1 ) ) = x → 0 lim exp ( sin x 1 ( − 2 x + 3 x 2 − 4 x 3 . . . ) ) = x → 0 lim exp ( x sin x 1 ( − 2 1 + 3 x − 4 x 2 . . . ) ) = e − 2 1
⟹ k = − 2 1