Multiple choice

If $\cos{\cfrac{\pi}{7}},\cos{\cfrac{3\pi}{7}},\cos{\cfrac{5\pi}{7}}$ are the roots of the equation $8{x}^{3}-4{x}^{2}-4x+1=0$ The value of $\tan ^{ 2 }{ \cfrac { \pi }{ 7 } } ,\tan ^{ 2 }{ \cfrac { 3\pi }{ 7 } } ,\tan ^{ 2 }{ \cfrac { 5\pi }{ 7 } } $ is

  1. ${x}^{3}-35{x}^{2}+7x-21=0$
  2. ${x}^{3}-35{x}^{2}+21x-7=0$
  3. ${x}^{3}-21{x}^{2}+35x-7=0$
  4. ${x}^{3}-21{x}^{2}+7x-35=0$
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