Answer to Question #90293 in Trigonometry for Michael

Question #90293

Cos3© is equivalent to

Expert's answer

"Cos(3x)=Cos(2x+x)=\\\\\n=Cos(2x)Cos(x)-Sin(2x)Sin(x)=\\\\\n=(Cos^2(x)-Sin^2(x))Cos(x)-2Sin(x)Cos(x)Sin(x)=\\\\\n=Cos^3(x)-3Sin^2(x)Cos(x)=\\\\\n=Cos^3(x)-3(1-Cos^2(x))Cos(x)=\\\\\n=4Cos^3(x)-3Cos(x)"

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