
Kenneth S. answered 12/02/17
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Expert Help in Algebra/Trig/(Pre)calculus to Guarantee Success in 2018
z = 25/2(-1 + i) = 25/2ei(¾)(pi)
or 25/2 [cos θ + i sin θ] where θ = (¾)(pi) + 2(pi)k, k = integer.
Therefore the three cube roots are 25/6[cos φ + i sin φ] for φ = = 450 or 165o or 285o
corresponding to k= 1, 2 or 2 and converting from radians to degrees, and using DeMoivre's theorem.