Hi

Got problem with these questions any suggestions?

Show that 2-i is a root of z^4 - 8z^3+28z^2-48z+35. Hence find all roots

and

Find all 5th roots of -32 and all 4th rots of 81i

In form x+iy where x and y in 4 DP

Thx

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- April 17th 2008, 05:21 AMNeloAngeloRoots
Hi

Got problem with these questions any suggestions?

Show that 2-i is a root of z^4 - 8z^3+28z^2-48z+35. Hence find all roots

and

Find all 5th roots of -32 and all 4th rots of 81i

In form x+iy where x and y in 4 DP

Thx - April 17th 2008, 05:30 AMbobak
all the coefficients of the quartic are real so the complex conjugate is a root.

so we have two factors and .

so is a factor of your quartic, divide your quartic by this factor and then solve the quadratic to get the two remaining roots.

Quote:

Find all 5th roots of -32 and all 4th rots of 81i

tell me how it goes

Bobak - April 21st 2008, 04:31 PMNeloAngelo
- April 21st 2008, 04:45 PMmr fantastic
Two things you

*should*know:

1. If is a root then is a linear factor.

2. If a polynomial has real coefficients and is a root, then , the conjugate of , is also a root.

Some of the questions you're asking suggest it would be a good thing for you to go back and thouroughly review this whole topic.