Answer:
[tex]\tan 2 x = \dfrac{24}7[/tex]
Step by step explanation:
[tex]\textbf{2)}\\\\\text{Given that,} \\\\~~~~~\cos x = -\dfrac 45\\\\\implies \cos^2 x = \dfrac{16}{25}~~~~~~~~~~;[\text{Square both sides}]\\\\\implies 1- \sin^2 x= \dfrac{16}{25}\\\\\implies \sin^2 x = 1- \dfrac{16}{25}\\\\\implies \sin^2 x = \dfrac{9}{25}\\\\\implies \sin x =\pm\sqrt{\dfrac{9}{25}}\\\\\implies \sin x = \pm \dfrac 35\\\\[/tex]
[tex]\text{Since,}~ \pi \leq x \leq \dfrac{3\pi}{2}, ~ \text{the angle lies in the 3rd quadrant, where}~ \sin x ~ \text{is negative.}\\\\\text{So,}~ \sin x = -\dfrac 35[/tex]
[tex]\text{Now,}~\\\\\tan x = \dfrac{\sin x }{\cos x} = \dfrac{-\tfrac 35}{-\tfrac 45} = \dfrac 35 \times \dfrac 54 = \dfrac 34\\\\\\\tan 2x =\dfrac{2 \tan x }{ 1- \tan^2 x}\\\\\\~~~~~~~~~=\dfrac{2 \left( \tfrac 34 \right)}{1- \left( \tfrac 34 \right)^2}\\\\~~~~~~~~~=\dfrac{\tfrac 64}{1-\tfrac {9}{16}}\\\\\\~~~~~~~~~=\dfrac{\tfrac 32 }{\tfrac 7{16}}\\\\\\~~~~~~~~~=\dfrac 32 \times \dfrac{16}7\\\\\\~~~~~~~~~=\dfrac{24}7[/tex]
