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## Homework Statement

The range of k for which the inequality ##k\cos^2x-k\cos x+1≥0## for all x, is

a. k<-1/2

b. k>4

c. -1/2≤k≤4

d. -1/2≤k≤2

## Homework Equations

## The Attempt at a Solution

I am not sure about how to begin with this. This seems to me a quadratic in cos(x) and here, the discriminant should be less than zero.

##k^2-4k<0##

This gives me ##0<k<4## but this is not given in any of the options.

Any help is appreciated. Thanks!