How to evaluate the limit of (cos x - cos 3x) / x*sin x if x-->0 ?

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We have to determine the value of lim x--> 0[(cos x - cos 3x) / x*sin x

If we substitute x = 0, we get

(1- 1) / 0 = 0/0

As this is an indeterminate form we use l'Hopital's rule...

(The entire section contains 102 words.)

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