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cos ^2x - 2cos X -1=0 use foil

The problem is:

cos ^2x - 2cos X -1=0

 

My answer was:

(cosx + 1)(cos(-x) - 1)

 

All wrong... Please help

 

 

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Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)
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You can solve it by completing the square.

cos^2 x - 2cos x + 1 = 2

(cos x - 1)^2 = 2

cos x = 1 - sqrt(2)

In (0, 2pi), x = 1.998 rad, 2pi-1.998 rad