How do you simplify #(-7i)(-3i)(-5-i)#?

2 Answers
Sep 27, 2016

#-105i^2-21i^3#

Explanation:

first multiply two of the terms*
#(-7i)(-3i)#

you now have
#21i²#

now multiply that with #(-5-i)#
#21i^2##(-5-i)#

you get
#-105i^2-21i^3#

*you can chose any two but these are easier

Sep 27, 2016

#105+21i#

Explanation:

Begin by multiplying the 2 leading terms.

#(-7i)(-3i)=21i^2=-21#

#color(orange)"Reminder " color(red)(bar(ul(|color(white)(a/a)color(black)(i^2=(sqrt(-1))^2=-1)color(white)(a/a)|)))#

The original question can now be expressed as.

#-21(-5-i)=105+21i#