How would you foil this?

Question

(-5+2i)(6-i)(4-3i)

Where i is the imaginary number square root of -1.

Answer 1

Best Answer - Chosen by Asker

First take any two of those polynomials and foil them together.

F -5 x 6
O -5 x -i
I 2i x 6
L 2i x -i

Now remember that when you get an i squared it just becomes -1.

After you get the first two polynomials foiled together, take that answer and foil it with the third polynomial.

It would look like

(-28 + 17i)(4-3i)

Then foil that out, remembering that i squared is -1 and you will get your answer.

Asker's Rating:

Asker's Comment:

Thank you! I almost got how to do this problem in this morning when I was half asleep, but this was very informative and took what I was thinking a step further. Thank you!

Answer 2

we start learning to multiply ordinary numbers
2 x 3 means 2 added 3 times

( 1+ 1) = 2 so ( 1 + 1) x 3 = (1 + 1) + (1 + 1) + (1 + 1)

Complex numbers are a new kind of number made of two parts:

( 2 + 3i) is ONE SINGLE ( ) number; made up of "2" the "real part"
and "3i" the "imaginary part. (real and imaginary are very very poor choices for the names)

the standard form is (a + bi)

the rules for addition are: (a + bi) = (c + di) = ( {a+c} + { b + d} i)

multiplication is longer
( ) x ( ) = (ac + adi + bci + bidi) but bidi = bdii= bd(-1)

so the final product is ({ac-bd} + {ad+bc}i

Check my work carefully, I might have made a mis type

Your problem has three ( ) complex numbers; the (6i) = (0 +6i)

do the first two than that product times the next.

It will be easier to multiply the (0 +6i) as the last term.

Try it each way three trys total. the answer must be the same for all

Practice, practice practice

this is a new but very powerful kind of math.

Source(s):

physics