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January 29, 2015

January 29, 2015

Posted by **greeny** on Thursday, July 26, 2012 at 11:26pm.

1 + i is a zero of f(x)= x4-2x^3-x^2 + 6x -6

I did synthetic division and I got that it wasnt a zero?

- math- finding zeros -
**MathMate**, Thursday, July 26, 2012 at 11:40pmThis is a trick question.

We know that complex roots always come in pairs. If 1+i is a root, so is 1-i, its conjugate.

The given root and its conjugate multiplied together become a real factor, namely (x-1-i)(x-1+i)=x^2-2*x+2.

Repeat your synthetic division using the combined real factor and you will have a quotient of x²-3.

- math- finding zeros -
**greeny**, Friday, July 27, 2012 at 12:06amoh yeah, I forgot about the conjugates! thanks!

One more question, how do i divide x^4-2x^3-x^2+6x-6 by x^2-2x+2 using synthetic division?

- math- finding zeros -
**MathMate**, Friday, July 27, 2012 at 6:34amIt's a similar process as long division with numbers.

Check out web resources such as:

http://www.purplemath.com/modules/synthdiv2.htm

or

http://www.youtube.com/watch?v=bZoMz1Cy1T4

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