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PLEASE HELP WITH MY TRIG HW: De Moivre's Theorem *Best Answer Awarded*?

PLEASE HELP! Best answer awarded

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  • Anonymous
    3 years ago
    Favorite Answer

    De Moivre's theorem states that if z = r(cos(x) + isin(x)) then z^n = r^n(cos(nx) + isin(nx))

    So first we write z = -3√3 + 3i in the form r(cos(x) + isin(x))

    r = √((-3√3)^2 + 3^2) = √(27 + 9) = √36 = 6

    sin(x) = 3/6 = 1/2 so x = 2πn + π/6 or x = 2πn + 5π/6

    cos(x) is negative, so π/2 < x < 3π/2

    so x = 5π/6

    so z = 6(cos(5π/6) + isin(5π/6))

    so z^5 = 6^5(cos(25π/6) + isin(25π/6))

    z^5 = 7776(cos(π/6) + isin(π/6))

    z^5 = 7776(√3/2 + i/2)

    z^5 = 3888√3 + 3888i

  • 3 years ago

    Let

    z=[-3sqr(3)+3i]^5

    =>

    z=(3^5)[-sqr(3)+i]^5----(1)

    Let z=243(z1)^5, where

    z1=-sqr(3)+i=>

    |z1|=sqr[3+1]=2=>

    z1=2[-sqr(3)/2+i/2]=>

    z1=2[cos(5pi/6)+isin(5pi/6)]

    =>

    (z1)^5=32[cos(25pi/6)+isin(25pi/6]

    (De Moivre's Theorem)

    =>

    (z1)^5=32[cos(pi/6)+isin(pi/6)]

    =>

    (z1)^5=32[sqr(3)/2+i/2]

    =>

    (z1)^5=16[sqr(3)+i]

    =>

    z=243(16)[sqr(3)+i]

    (from (1))

    =>

    z=3888[sqr(3)+i]

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