4 cos(θ + 60◦) cos(θ + 30◦) ≡ √3 − 2 sin 2θ
Given that there are no values of θ which satisfy the equation4 cos(θ + 60◦) cos(θ + 30◦) = k,determine the set of values of the constant k.
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I've made sin2θ -1 and 1,
So the minimum of the graph at sin2θ=-1 gives √3+2 and the maximum of the graph at sin2θ= 1 gives √3-2
So for there to be no values k<√3+2 and k>√3-2
But this is wrong on the mark scheme - they're meant to be the other way round.
Where have I gone wrong?