Cos(x-10)+cos(x+10)=0

[latex]cos(x-10)+cos(x+10) = 0[/latex] [latex]cos(x)cos10 + sin(x)sin10 + cos(x)cos10 - sin(x)sin10 = 0[/latex] [latex]cos(x)cos10 + cos(x)cos10 = 0[/latex] [latex]cos(x) = 0[/latex] x ∈ π/2 + 2πn, n ∈ Z

cos(x-10)=sin alfa/cos alfa