math
posted by Anonymous .
write the expression 5i(1 + 3i) as a complex number in standard form.

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)