Verified Solution • 2025–26 Session moderate

QJEEM19Ma4605: JEE Main 2019 Mathematics - Class 11 JEEM19Ma4605 Solution: If cos( + ) = 3/5 ,sin ( - ) = 5/13 and 0 < < , then tan(2 ) is …

If cos( α\alpha + β\beta ) = 3/5 ,sin ( α\alpha - β\beta ) = 5/13 and 0 < α,β\alpha , \beta < π4\pi \over 4 , then tan(2 α\alpha ) is equal to :

Multiple Choice Options

  • A 21/16
  • B 63/52
  • C 33/52
  • D 63/16

Step-by-Step Verified Solution

Given 0 &lt; \alpha &lt; {\pi \over 4}

and 0 &lt; \beta &lt; {\pi \over 4}

∴\therefore 0 &gt; - \beta &gt; - {\pi \over 4}

∴\therefore 0 &lt; \alpha + \beta &lt; {\pi \over 2}

and - {\pi \over 4} &lt; \alpha - \beta &lt; {\pi \over 4}

As cos( α\alpha + β\beta ) = 3/5

so tan⁡(α+β)=43{\tan \left( {\alpha + \beta } \right) = {4 \over 3}}

As sin( α\alpha - β\beta ) = 5/13

so tan⁡(α−β)=512{\tan \left( {\alpha - \beta } \right) = {5 \over {12}}}

Now tan(2 α\alpha ) = tan( α\alpha + β\beta + α\alpha - β\beta )

= tan⁡(α+β)+tan⁡(α−β)1−tan⁡(α+β)tan⁡(α−β){{\tan \left( {\alpha + \beta } \right) + \tan \left( {\alpha - \beta } \right)} \over {1 - \tan \left( {\alpha + \beta } \right)\tan \left( {\alpha - \beta } \right)}}

= 43+5121−43×512{{{4 \over 3} + {5 \over {12}}} \over {1 - {4 \over 3} \times {5 \over {12}}}} = 6316{{63} \over {16}}

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