(4+20i) and (4-5i) 5/6/2014 | Esli from Whittier, CA | 2 Answers | 0 Votes Mark favorite Subscribe Comment
use the distributive property (4 + 20i)(4-5i)= 4(4-5i) + 20i(4-5i) get rid of parenthesis 16 -20i + 80i -100i^{2} i^{2}=-1 substitute and group like terms then simplify 16 + -100(-1) + i(-20 + 80) 116 + 60i 5/15/2014 | PAT T. Comment
(4+20i) x (4-5i) factor out the 4 out 4( 1+5i) (4-5i) multiply all the parts together [4]x[1x4 + 1x(-5i) +(5i)x4 + (5i)(-5i)] You multiply complex numbers similar to the way toy multiply binomials. =[4]x[ 4 - 5i + 20i -25] = 4(29+15i) 5/6/2014 | Robert A. Comment