Simplify (1-2i)(1-i)(1+i)(1+2i)
(1-2i)(1-i)(1+i)(1+2i) =
(1 + 2i) (1 - 2i) (1+ i) (1 - i) =
(1 - 4i^2) ( 1 - i^2) [ remember that i^2 = - 1 ]
(1 - 4(-1) ) ( 1 - (-1) ) =
( 1 + 4) (1 + 1) =
5 * 2 =
10
