Question #79b74

1 Answer
P dilip_k
Apr 5, 2017

2cos2x-4cosx=1

=>2(2cos^2x-1)-4cosx=1

=>4cos^2x-2-4cosx=1

=>(2cosx)^2-2*cosx*1+1^2=1+2+1

=>(2cosx-1)^2=4

=>2cosx-1=pm2

So

cosx=(2+1)/2=1.5>1->"not possible"

Again

cosx=(-2+1)/2=-1/2=cos(pi-pi/3)

=>cosx=cos((2pi)/3)

=>x=2npipm(2pi)/3" where "n in ZZ

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