Given-that-x-R-the-set-of-real-numbers-d-an-n-N-the-set-of-positive-naturalu-nmbers-prove-that-cos-x-cos-2x-cos-3x-cos-n-1-x-n-2-

Question Number 212492 by MrGaster last updated on 15/Oct/24

Given that x \in R (

(the set of real numbers) d

an n \in N^{*}

(the set of positive naturalu

nmbers) prove that :

∣ \cos x ∣ + ∣ \cos 2 x ∣ + ∣ \cos 3 x ∣ + \dots + ∣ \cos (n + 1) x ∣\geq \frac{n}{2}