If #cos(x)cos(x-60°)=1-(n/6)#, so n = ?

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Answer 1 · 2017-11-24T16:10:50

#cos(x)cos(x-60°)=1-(n/6)#

#=>2cos(x)cos(x-60°)=2-(n/3)#

#=>cos(2x-60)+cos(60°)=2-(n/3)#

#=>cos(2x-60)+1/2=2-(n/3)#

#=>cos(2x-60)=2-1/2-(n/3)#

#=>cos(2x-60)=3/2-n/3#

as #1<=cos(2x-60)<=+1#

we get

#-1<=3/2-n/3<=+1#

#=>-1-3/2<=3/2-3/2-n/3<=+1-3/2#

#=>-5/2<=-n/3<=-1/2#

#=>5/2>=n/3>=1/2#

#=>5/2xx3>=n/3xx3>=1/2xx3#

#=>7.5>=n>=1.5#