write the expression -5i(1 + 3i) as a complex number in standard form.

Answer 1

well, break it up:

-5i : 5@-90
1+3i: sqrt10 @arctan3

now multiply them

5sqrt10 @(-90+71.56) now that angle, after adding 360, is 341.56

5sqrt10 (.9486 -316i)