We have to find the value of lim x--> 90[ (1- sin x)/(cos x)^2]
substituting x = 90 degrees, we get the indeterminate form 0/0, so we can use l'Hopital's rule and substitute the numerator and denominator by their derivatives.
=> lim x->90 [ (- cos x)/ (-2 cos x * sin x)]
=> lim x->90 [ 1/ (2 sin x)]
substitute x = 90
=> 1/ 2
The required value of lim x--> 90[ (1- sin x)/(cos x)^2] is (1/2).
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