2cosX-cos(квадратный)X=0

Question

2cosX-cos(квадратный)X=0

Answer 1

2.cosx -cos²x=0
cosx(2-cosx)=0
a)cosx=0, x=π/2+k.π , k∈Z
b)2-cosx=0, cosx=2, /cosx/≤1, x∈∅

x=π/2+k.π, k∈Z
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