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• When you use l'hopital's rule, you first need to make sure you get an indeterminate form. If that's the case (which it is here), take the derivative of the top and the derivative of the bottom. If you still get an indeterminate form, do it again. …

  in lim[x approaches 0, (1-cos5x)/(7x^2)]? Comment by george-harrison_6098576104247 May 2021