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 $={2.3462,3.937) sub [0,2pi].$