If ${e^{\cos x}} - {e^{ - \cos x}} = 4$ then the value of $\cos x$ is

JEE MATHEMATICS MCQ: QUADRATIC EQUATIONS

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Application +4 | -1

{e^{\cos x}} - {e^{ - \cos x}} = 4

then the value of

\cos x

View answer and explanation

Correct option: A

\log \left( {2 + \sqrt 5 } \right)

Option A (

\log \left( {2 + \sqrt 5 } \right)

) is correct because by substituting

y = e^{\cos x}

into the equation and solving the quadratic, we find that

\cos x = \log(2 + \sqrt{5})

Practice All Chapter MCQs →

\log _7 \log _5(\sqrt{x+5}+\sqrt{x})=0

\alpha ,\beta

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{x^2} - px + q = 0

{\alpha _1},{\beta _1}

{x^2} - qx + p = 0,

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{x^2} + 4ax + 2 > 0

x

a

f\left( x \right) = a{x^2} + bx + c\;

\;f\left( { - 1} \right) < 1,f\left( 1 \right) > - 1,f\left( 3 \right) < - 4\;

\;a \ne 0,

9{x^2} - 18\left| x \right| + 5 = 0

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