How do you simplify this answer, keeping in mind that we are working with imaginary numbers? (8i)(4i)(-9i)

Question

Do you use a different version of FOIL?

Do you just multiply 8x4x(-9)?

or do you multiply 8iX4i which equals 32 but then mutliply it by -1 because i^2=-1 so you'd have -32, and then multiply that by -9i which would equal -288i. Is that the final answer?

Answer 1

Actually Ashley forgot to cube the i terms, not just multiply the coefficients. If you multiply this out you get -288i³

 

i3= -i

 

so -288(-i) = 288i

 

i = √-1

 

so the answer is 288i or 288√-1

Answer 2

Rachel,

 

When multiplying (8i)(4i)(9i), you can multiply (8i)(4i), which is equal to -32. You then multiply (-32)(9i), which equals -288i. However, if you chose to multiply (4i)(9i) = -36, and then multiply (-36)(8i) you also get -288i.

 

-288i is the final answer.