Question #e6469

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Answer 1 · 2016-06-24T18:47:09

#x=128°#

By multiplying, you obtain:

#(cos^2x-1)/cos^2x=1/cosx#

that is equivalent to:

#(cos^2x-1)/cos^2x=cosx/cos^2x#

and, by fixing #cosx!=0#,

#cos^2x-1-cosx=0#

#cos^2x-cosx-1=0#

#cosx=(1+-sqrt(1+4))/2#

#cosx=(1+-sqrt(5))/2#

#cosx=(1+sqrt(5))/2# is impossible

#cosx=(1-sqrt(5))/2#

#x=128°#