I need help showing that \(\displaystyle{\left({4}{\sin{\theta}}\right)}{\left({\sin{{\left(\theta-{\frac{{\pi}}{{{3}}}}\right)}}}\right)}{\left({\sin{{\left(\theta-{\frac{{{2}\pi}}{{{3}}}}\right)}}}\right)}={\sin{{\left({3}\theta\right)}}}\)

parksinta8rkv

parksinta8rkv

Answered question

2022-03-31

I need help showing that (4sinθ)(sin(θπ3))(sin(θ2π3))=sin(3θ)

Answer & Explanation

Sawyer Anthony

Sawyer Anthony

Beginner2022-04-01Added 10 answers

Expand both sides. Left side:
4sinθ(sinθcosπ3cosθsinπ3)(sinθcos2π3cosθsin2π3)
Use complementary angles:
=4sinθ(sinθcosπ3cosθsinπ3)(sinθcosπ3cosθsinπ3)
Difference of squares:
=4sinθ(sin2θcos2π3cos2θsin2π3)
=4sinθ(sin2θcos2π3(1sin2θ)sin2π3)
=4sinθ(sin2θsin2π3)
=4sinθ(sin2θ34)
=3sinθ4sin3θ
Right side:
sin3θ=sinθcos2θ+cosθsin2θ
=sinθ(cos2θsin2θ)+2cos2θsinθ
sinθ(12sin2θ)+2(1sin2θ)sinθ
=3sinθ4sin3θ

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