Answer:
180degreesStep-by-step explanation:
Given the complex value
z² = -81i
z = (-81i)^1/2
Get the argument of -81i
theta = arctan(y/x)
theta = arctan(-81/0)
theta = -90degrees
theta = -π/2
Since tan is negative in the secind quadrant
theta = π - π/2
theta = π/2
According to demoivres theorem
theta = 1/2 * π/2
theta = π
theta = 180degrees