(4+20i) and (4-5i)

## Which is the product of the complex number (4+20i) and (4-5i)

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# 2 Answers

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 simplify16 + -100(-1) + i(-20 + 80)

116 + 60i

(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)