Question:

The integral $ \int\limits^{1/2}_{-1/2} \bigg ([x] + \log \bigg ( \frac{1+ x}{1 - x} \bigg ) \bigg ) \, dx $ equals

Updated On: Jun 14, 2022
  • $-\frac{1}{2}$
  • 0
  • 1
  • $log \bigg ( \frac{1}{2} \bigg )$
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The Correct Option is A

Solution and Explanation

$ \int ^{1/2}_{-1/2} \bigg ([x] + log \bigg ( \frac{1+ x}{1 - x} \bigg ) \bigg ) \, dx \, $
$ = \int^{1/2}_{-1/2} [x] \, dx + \int^{1/2}_{-1/2} \, log \bigg (\frac{1+ x }{1 - x } \bigg ) dx $
$ = \int^{1/2}_{-1/2} [x] \, dx + 0 \, \, \, \, \, \, \, \, \, \, \, \, \, \, \bigg [\because \bigg ( \frac{ 1 + x }{ 1 - x} \bigg ) $ is an odd function $\bigg ]$
$ = \int^{0}_{-1/2} [x] \, dx + \int^{1/2}_{0} [x] \, dx = \int^{0}_{-1/2} ( - 1) \, dx + \int^{1/2}_{0} \, dx$
$=[ x]^0_{-1/2} = - \bigg ( 0 + \frac{1}{2} \bigg ) =- \frac{1}{2}$
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Questions Asked in JEE Advanced exam

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Concepts Used:

Integration by Parts

Integration by Parts is a mode of integrating 2 functions, when they multiplied with each other. For two functions ‘u’ and ‘v’, the formula is as follows:

∫u v dx = u∫v dx −∫u' (∫v dx) dx

  • u is the first function u(x)
  • v is the second function v(x)
  • u' is the derivative of the function u(x)

The first function ‘u’ is used in the following order (ILATE):

  • 'I' : Inverse Trigonometric Functions
  • ‘L’ : Logarithmic Functions
  • ‘A’ : Algebraic Functions
  • ‘T’ : Trigonometric Functions
  • ‘E’ : Exponential Functions

The rule as a diagram: