If-e-cos-x-e-cos-x-4-then-the-value-of-cos-x-is-

Question Number 86507 by ram roop sharma last updated on 29/Mar/20

If e^{\cos x} - e^{- \cos x} = 4, then the value

of \cos x is

Commented by jagoll last updated on 29/Mar/20

{(e^{\cos x})}^{2} - 1 = {4 e}^{\cos x}

{(e^{\cos x} - 2)}^{2} = 5

e^{\cos x} = 2 + \sqrt{5}

\cos x = \ln (2 + \sqrt{5}) > 1

\cos x = \ln (2 - \sqrt{5}) < - 1

\cos x = \emptyset, in x \in R

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