How to Simplify \(\displaystyle{\frac{{{\sin{{\left({3}{x}\right)}}}+{{\sin}^{{3}}{\left({x}\right)}}}}{{{\cos{{\left({3}{x}\right)}}}-{{\cos}^{{3}}{\left({x}\right)}}}}}\) I tried to: \(\displaystyle{\frac{{{\sin{{\left({2}{x}\right)}}}{\cos{{\left({x}\right)}}}+{\cos{{\left({2}{x}\right)}}}{\sin{{\left({x}\right)}}}+{{\sin}^{{3}}{\left({x}\right)}}}}{{{\cos{{\left({2}{x}\right)}}}{\cos{{\left({x}\right)}}}+{\sin{{\left({2}{x}\right)}}}{\sin{{\left({x}\right)}}}-{{\cos}^{{3}}{\left({x}\right)}}}}}\)

Izabelle Walsh

Izabelle Walsh

Answered question

2022-04-06

How to Simplify sin(3x)+sin3(x)cos(3x)cos3(x)
I tried to:
sin(2x)cos(x)+cos(2x)sin(x)+sin3(x)cos(2x)cos(x)+sin(2x)sin(x)cos3(x)

Answer & Explanation

Drantumcem0

Drantumcem0

Beginner2022-04-07Added 10 answers

With one step further you have
sin(3x)=4sin3x+3sinx  and  cos3x=3cosx+4cos3x
that is
sin(3x)+sin3x=3sinx(1sin2x)=3sinxcos2x
and
cos3xcos3x=3cosx(1cos2x)=3cosxsin2x
Then
sin(3x)+sin3(x)cos(3x)cos3(x)=3sinxcos2x3cosxsin2x=cotx
gil001q4wq

gil001q4wq

Beginner2022-04-08Added 11 answers

Note that
cos(3x)+isin(3x)=(cos(x)+isin(x))3
=cos3(x)+3icos2(x)sin(x)3cos(x)sin2(x)isin3(x)
Therefore, after separating real and complex parts, we obtain
cos(3x)=cos3(x)3cos(x)sin2(x),sin(3x)=3cos2(x)sin(x)sin3(x)
Finally
sin(3x)+sin3(x)cos(3x)cos3(x)=3cos2(x)sin(x)3cos(x)sin2(x)=cos(x)sin(x)=cot(x)

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