How do you use DeMoivre's theorem to simplify (-sqrt3-i)^4?

1 Answer
Sep 10, 2016

- 8 + 8 sqrt(3) i

Explanation:

We have: (- sqrt(3) - i)^(4)

First, let's consider the complex number z = - sqrt(3) - i.

In order to apply De Moivre's theorem, we need to evaluate the modulus and argument of this z:

=> |z| = sqrt((- sqrt(3)^(2) + (- 1)^(2))

=> |z| = sqrt(3 + 1)

=> |z| = sqrt(4)

=> |z| = 2

=> theta = arctan((- 1) / (- sqrt(3)))

=> theta = arctan((sqrt(3)) / (3))

=> theta = (pi) / (6)

Then, z is located in the third quadrant:

Rightarrow arg(z) = pi / 6 - pi = - (5 pi) / 6

So, z = 2 (cos(- (5 pi) / 6) + i sin(- (5 pi) / 6))

Now, using De Moivre's theorem:

=> z^(4) = 2^(4) (cos(4 cdot - (5 pi) / 6) + i sin(4 cdot - (5 pi) / 6))

=> z^(4) = 16 (cos(- (10 pi) / (3)) + i sin(- (10 pi) / (3)))

=> z^(4) = 16 (- (1) / (2) + (sqrt(3)) / (2) i)

=> z^(4) = 16 (- (1) / (2) (1 - sqrt(3) i))

=> z^(4) = - 8(1 - sqrt(3) i)

therefore z^(4) = - 8 + 8 sqrt(3) i

Therefore, (- sqrt(3) - i)^(4) = - 8 + 8 sqrt(3) i.