Hey guys i was working through this question and when i cheked my answers i realised there was an extra bit to do to get the final answer but i dont know wt im supposed to do:

Q) Express (-1 + sqrt3i) in modulus-argument form. Evaluate (-1 + sqrt3i)^8,

expressing your answer in a + ib form.

I got z= 2cis 2pi/ 3 for mod -arg form but when i evaluate it I can get to:

2^8 cis 16pi/3

but then the answers tell me tht the answer above is equal to 2^8 cis 4pi/3???

And that the final answer in a+ ib form is : -128 - 128sqrt3i .

What i want to know is how do i go from 2^8 cis 16pi/3 ==> -128 - 128 sqrt3i??