1.

Th range of k for which the inequaliity `kcos^2x-kcosx+1>=0 AA x in(-oo,oo) is`A. `klt- 1/2`B. `kgt4`C. `-1/2lekle4`D. `1/2lekle5`

Answer» Correct Answer - C
`kcos^2x-kcos+1le0AAx in(-oo,oo)`
`rArrk(cos^2x-cosx)+1ge0`
But `cos^2x-cosx=(cosx-1/2)^2-1/4`
`rArr -1/4lecos^2x-cosxle2`
Now, from (i), we get `2k+1ge0rArr kge-1/2`
Also, `-k/4+1ge0`
`rArr kle4`
`rArr -1/2lekle4`


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