How do you solve #(\cos x ) ^ { 2} - 1.3\cos x - 1.98= 0#?

1 Answer
Gerardina C.
Mar 16, 2017

#x~=154.16° or x~=205.84°#

Explanation:

You would apply the quadratic formula to find #cosx#:

#cosx=(1.3+-sqrt(1.3^2-4*(-1.98)))/2#

#=(1.3+-3.1)/2#

You cannot admit the solution #cosx=2.2#, then the one solution is #cosx=-0.9->x~=154.16° or x~=205.84°#

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