How do I expand \(\displaystyle{{\sin}^{{5}}\theta}\) using the

meli199939f

meli199939f

Answered question

2022-03-26

How do I expand sin5θ using the complex exponential, in order to obtain:
116sin5θ516sin3θ+58sinθ

Answer & Explanation

horieblersee275

horieblersee275

Beginner2022-03-27Added 17 answers

Using this formula.
exp(iθ)n=exp(niθ)
(cos(θ)+isin(θ))n=cos(nθ)+isin(nθ)
(cos(θ)+isin(θ))5=cos(5θ)+isin(5θ)
cos5(θ)sin4(θ)+isin5(θ)=cos(5θ)+isin(5θ)
Equate imaginary parts:
5cos4(θ)sin(θ)=10cos2(θ)sin3(θ)+sin5(θ)=sin(5θ)
Solve for sin5(θ)
sin5(θ)=sin(5θ)5cos4(θ)sinθ+10cos2(θ)sin3(θ)
Use trigonometric identities:
sin5(θ)=116(sin(5θ)5sin(3θ)+10sin(θ))

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