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April 21, 2014

April 21, 2014

Posted by **annaiiz** on Wednesday, April 1, 2009 at 9:56pm.

question is: 1-2i+i^3/1+i

this is what i did:

1-2i+i(-i)/1+i

1-2i-i^2/1+i

1-2i-i(-1)/1+i

1-2i+i/1+i

1-3i/1+i*1-i/1-i

1-i-3i+3i^2/1-i+i-i^2

1-i-3i+3(-1)/1-i^2

1-i-3i-3/1-(-1)

1-4i-3/2

-2-4i/2

my answer is -2i-1

is that right?

- math help people lik really desperate!! -
**carpediem**, Wednesday, April 1, 2009 at 10:07pmBe more specific with parentheses. Does the 1+i divide into only the i^3 term? Or does it divide into 1 - 2i + i^3?

- math help people lik really desperate!! -
**Reiny**, Wednesday, April 1, 2009 at 10:32pmfrom what you showed in your work I will asssume you meant

(1-2i+i^3)/(1+i)

you messed up in your first line.

remember i^3 = i(i^2) = i(-1) = -i

so

(1-2i+i^3)/(1+i)

= (1-2i - i)/1+i)

= (1-3i)/(1+i)

now multiply top and bottom by 1-i to get

(1-4i - 3i^2)/(1 - i^2)

= (4-4i)/2

= 2 - 2i

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