Question #d3232

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Answer 1 · 2016-10-01T14:13:57

#"The Soln. Set="{2.3462,3.937) sub [0,2pi].#

Observe that, #(1.3)(0.7)=0.91, and, 1.3-0.7=0.6#, so,

#cos^2x-0.6cosx-0.91=0#

#rArr ul(cos^2x-1.3cosx)+ul(0.7cosx-0.91)=0#

#rArr cosx(cosx-1.3)+0.7(cosx-1.3)=0#

#rArr (cosx-1.3)(cosx+0.7)=0#

#rArr cosx=1.3, cosx=-0.7#

But, since, #cosxle1.0, cosx!=1.3#

#:. cosx=-0.7#

#:. x=cos^-1(-0.7)=pi-cos^-1(0.7)~~2.3462#

Also, #x=pi+cos^-1(0.7)~~3.937# is a soln.

Hence, the Soln. Set#={2.3462,3.937) sub [0,2pi].#