Given \ \

cos ^ 2 ( x ) - 5 cos ( x )  - 1 = 0 and interval [ 0 , 2 ∏ ] \ \

Compare to the quadratic equation form a ^ 2 x + b x  +  c. \ \

a = 1 , b = - 5 and c = - 1. \ \

Substituting the a, b and c values \ \

\ \

  \ \

cos ^ 2 ( x ) - 5 cos ( x )  - 1 = 0 and interval [ 0 , 2 ∏ ] \ \

Solution : \ \

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