h → 0 lim h e 2 h − 1 = ?
Bonus: Don't use the hospital.
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Can you think of a simpler approach? Hint: What is the definition of a derivative? Define f ( x ) = e 2 x . What does x − 0 e 2 x − e 2 ⋅ 0 mean? Slope is the ratio of rise and run.
Thanks. Ishan has shown it.
I did it the same way. e^(2h) is just 1+2h plus a bunch of higher order terms, so clearly (1+2h-1)/h=2
By the difference of two squares, e 2 h − 1 = ( e h + 1 ) ( e h − 1 ) , so h → 0 lim h e 2 h − 1 = 2 × h → 0 lim h e h − 1 , because e 0 + 1 = 2 . But, remember your calculus 1 classes? The derivative of a exponential function is, by definition, d x d n x = h → 0 lim h n x + h − n x = n x × h → 0 lim h n h − 1 , and, by definition, e is the number which h → 0 lim h n h − 1 = 1 , in order to find the exponencial function which is its own derivative. So, 2 × h → 0 lim h e h − 1 = 2 × 1 = 2 .
Let 2h=t,as h->0 t->0 then it becomes 2lim e^t -1/t = 2 as t->0
Cheat, use a sci calculator and set h = to a small value, say .001, and calculate directly.
It is known that h → 0 lim h e h − 1 = 1 (don't trust me? Check a proof for e x being its own derivative). Now, h → 0 lim h e 2 h − 1 = h → 0 lim h e h − 1 ⋅ ( e h + 1 ) = h → 0 lim h e h − 1 ⋅ h → 0 lim ( e h + 1 ) = 1 ⋅ ( 1 + 1 ) = 2 .
Assuming the fact that you used, there is a much more direct approach that allows you to generalize to all real values r . What is
h \righarrow 0 lim h e r h − 1 ?
P.S. Actually, for the fact that you stated, the limit is just h e h − 1 . Be careful what you are taking limits with respect to :)
Thanks! Already corrected that. :)
The Taylor expansion of e x about x = 0 is
n = 0 ∑ ∞ n ! x n
The first two terms of the expansion of e 2 h are 1 + 2 h which gives h 1 + 2 h − 1 = h 2 h = 2
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We can use Maclaurin series as follows:
h → 0 lim h e 2 h − 1 = h → 0 lim h ( 1 + 2 h + 2 ! ( 2 h ) 2 + 3 ! ( 2 h ) 3 + . . . ) − 1 = h → 0 lim ( 2 + 2 ! 2 2 h + 3 ! 2 3 h 2 + 4 ! 2 4 h 3 + . . . ) = 2