lim (tanx - sinx / x^3 ) = ?
x->0
I tried to do lopital , but, I did was stuck somewhere... I got 1/4.. the
lim (tanx - sinx / x^3 ) = ?
x->0
I tried to do lopital , but, I did was stuck somewhere... I got 1/4.. the
Is that or what you have typed:
I assume the former. Grouping symbols are important.
You can use L'Hopital, but it requires several applications.
First application:
second application:
Third application:
Now, letting x=0 in the numerator, we get:
Here is a non-L'Hopital way to go about it. I like this better.
Rewrite as:
Now, take each limit separately.
Now for:
From the first limit we have 1. So, we get
Thus, the limit is 1/2
Note that is a famous limit used often when proving other limits. It is not necessary to prove it here, but use it as a lemma, so to speak. It's proof usually involves the Squeeze Theorem.
As for , we can use an approximation. Knowing that for x near 0, we can sub this in and get:
.
Now, as can be seen, as , we are left with 1/2.
Actually, we could have used this approximation, as well as for x near 0, to prove from the outset.
Doing so, leads to
Now, as , we are left with... again... 1/2.
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When dealing with trig limits with , then the following approximations will prove useful.
These are known as 'asymptotic' approximations.
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