SOLUTION: Find the polynomial equation, P(x)=0, of the least possible degree, with integral coefficients, and whose roots are a.) 3 + 2i; 1 - √3 and -1 b.) -1, 3/2, and ³&#873

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: Find the polynomial equation, P(x)=0, of the least possible degree, with integral coefficients, and whose roots are a.) 3 + 2i; 1 - √3 and -1 b.) -1, 3/2, and ³&#873      Log On


   



Question 933563: Find the polynomial equation, P(x)=0, of the least possible degree, with integral coefficients, and whose roots are
a.) 3 + 2i; 1 - √3 and -1
b.) -1, 3/2, and ³√5 (the cube root of 5).

Answer by Edwin McCravy(20060) About Me  (Show Source):
You can put this solution on YOUR website!
3+2i; 1-√3 and -1

For a polynomial to have integral coefficients, if it has a root
of the form a+bi, it also has a-bi as a root, and vice-versa.
Alos if a polynomial has a root of the form a+√b, it also 
has a-√b as a root, and vice-versa.

So the complete set of roots are

3+2i, 3-2i, 1-√3, 1-√3 and -1.

We make 5 equations with x= before each one:

x=3+2i, x=3-2i, x=1-√3, x=1+√3, x=-1

Get zero on the right of each one:

x-3-2i=0, x-3+2i=0, x-1+√3=0, x=1-√3, x+1=0

Then we multiply equals by equals:

(x-3-2i)(x-3+2i)(x-1+√3)(x-1-√3)(x+1)=0

Then you multiply that out.  You can make
it a little easier by grouping like this:

[(x-3)-2i][(x-3)+2i][(x-1)+√3][(x-1)-√3](x+1)=0

But it's a big job.  I won't go through the
details here, to let you get some practice.  
The result is:

%22P%28x%29%22+=+x%5E5-7x%5E4%2B15x%5E3%2B9x%5E2-40x-26+=+0

---------------------------------------

The other one has a fraction and a cube root.

x=-1,x=3%2F2, x=root%283%2C5%29

In this one, before you mutiply them you must get them so that
there are no fractions or cube roots, only integers.
So you must clear x=3%2F2 of fractions, getting 2x=3 
and cube both sides of x=root%283%2C5%29, getting x%5E3=5

So you have these 

x=-1,2x=3, x%5E3=5

Get 0 on the right of each:

x%2B1=0,2x-3=0, x%5E3-5=0

Multiply equals by equals:

%28x%2B1%29%282x-3%29%28x%5E3-5%29=0

Multiply that out and the result is

%22P%28x%29%22=2x%5E5-x%5E4-3x%5E3-10x%5E2%2B5x%2B15

Edwin