The number
cis 75∘+cis 83∘+cis 91∘+⋯+cis 147∘
is expressed in the form rcis θ, where 0≤θ<360∘. Find θ in degrees.
Hint: cis θ=cosθ+isinθ
Edit:
I simplified the expression down to
cis 75∘sin40∘ cis 40∘sin4∘ cis 4∘.
What should I do now?

Respuesta :

The value of the angle θ in the rcis θ be 16 degrees.

Given, a number rcis θ, is expressed by

cis 75° + cis 83° + cis 91° + ⋯ + cis 147°

we have to find the value of θ in degrees

Now, we have to find the sum of the given expression

cis 75° + cis 83° + cis 91° + ⋯ + cis 147°

as, cis θ = e^iθ

e^i75° + e^i83° + e^i91° + ⋯ + e^i147°

e^i75π/180 + e^i83π/180 + e^i91π/180 + ⋯ + e^i147π/180

On using the geometric sum of the Geometric Progression, we get

Sum = e^i75π/180(1 - e^i72π/180)/(1 - ei^8π/180)

r cis θ = cos θ + i sin θ

θ = 16°

The value of the angle θ be 16 degrees.

Hence, the value of the angle be 16 degrees.

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