1.

Write the solution set of the equation `(2costheta+1)(4costheta+5)=0`in the interval `[0,2pi]`

Answer» `(2costheta+1)(4costheta+5) = 0`
`=>(2costheta+1) = 0 or (4costheta+5) = 0`
`=>costheta = -1/2 or cos theta = -5/4`
But, minimum value of `cos theta` is `-1`, so `costheta != -5/4.`
`:. costheta = -1/2`
`=>theta = (2pi)/3,(4pi)/3.`


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