Question

write a polynomial function with the zeros 1, -2i

Answer 1

f( x ) = ( x - 1 ) ( x + 2i )( x - 2i ), because the zeroes are 1, -2i, +2i ;
f( x ) = ( x - 1 )( x^2 - 4i^2 ) = ( x - 1 )( x^2 + 4 ) = x^3  - x^2 + 4x - 4 ;