Verified Solution • 2025–26 Session moderate

QJEEM19Ma6d99: JEE Main 2019 Mathematics - Class 12 JEEM19Ma6d99 Solution: If    then value of k is :

If    \int\limits_0^{{\pi \over 3}} {{{\tan \theta } \over {\sqrt {2k\,\sec \theta } }}} \,d\theta = 1 - {1 \over {\sqrt 2 }},\left( {k > 0} \right), then value of k is :

Multiple Choice Options

  • A 4
  • B 12{1 \over 2}
  • C 1
  • D 2

Step-by-Step Verified Solution

\int\limits_0^{{\pi \over 3}} {{{\tan \theta } \over {\sqrt {2k\,\sec \theta } }}} \,d\theta = 1 - {1 \over {\sqrt 2 }},\left( {k > 0} \right),

\Rightarrow \,\,\int\limits_0^{\pi /3} {{{\tan \theta } \over {\sqrt {2k\sec \theta } }}} \,d\theta = 1 - {1 \over {\sqrt 2 }}\left( {k > 0} \right)

⇒  12k(−2cos⁡θ)0π/3=1−12\Rightarrow \,\,{1 \over {\sqrt {2k} }}\left( { - 2\sqrt {\cos \theta } } \right)_0^{\pi /3} = 1 - {1 \over {\sqrt 2 }}

⇒  12k(−2+2)=1−12\Rightarrow \,\,{1 \over {\sqrt {2k} }}\left( { - \sqrt 2 + 2} \right) = 1 - {1 \over {\sqrt 2 }}

⇒  2(2−1)2k=2−12\Rightarrow \,\,{{\sqrt 2 \left( {\sqrt 2 - 1} \right)} \over {\sqrt {2k} }} = {{\sqrt 2 - 1} \over {\sqrt 2 }}

⇒  k=2\Rightarrow \,\,k = 2

Related Learning Resources & Exam Preparation