2(Sin78⁰Cos18⁰ + Sin168⁰Sin198⁰) = 2(Sin78⁰Cos18⁰ +
+ Sin(90⁰ + 78⁰)Sin(180⁰ +18⁰)) = 2(Sin78⁰Cos18⁰ - Cos78⁰Sin18⁰) =
= 2Sin(78⁰ - 18⁰) = 2Sin60⁰ = 2 * √3/2 = √3
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2(Sin78⁰Cos18⁰ + Sin168⁰Sin198⁰) = 2(Sin78⁰Cos18⁰ +
+ Sin(90⁰ + 78⁰)Sin(180⁰ +18⁰)) = 2(Sin78⁰Cos18⁰ - Cos78⁰Sin18⁰) =
= 2Sin(78⁰ - 18⁰) = 2Sin60⁰ = 2 * √3/2 = √3