SOLUTION: Find a 4th degree polynomial equation with integer coefficients which has two irrational roots, one of which is 2+3{{{sqrt(5)}}}, and two imaginary roots, one of which is 3-2i.

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: Find a 4th degree polynomial equation with integer coefficients which has two irrational roots, one of which is 2+3{{{sqrt(5)}}}, and two imaginary roots, one of which is 3-2i.       Log On


   



Question 570679: Find a 4th degree polynomial equation with integer coefficients which has
two irrational roots, one of which is 2+3sqrt%285%29, and two imaginary
roots, one of which is 3-2i.

Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
Find a 4th degree polynomial equation with integer coefficients which has 
two irrational roots, one of which is 2+3sqrt%285%29, and two imaginary
roots, one of which is 3-2i.

In order to have integer coefficients if a polynomial equation has
the irrational root A%2BB%2Asqrt%28C%29, it must also have its conjugate
A-B%2Asqrt%28C%29.  Similarly if it has an imaginary root C+Di as a root,
it must also have its conjugate C-Di as a solution. 

So, since it must have integer coefficients, and 2+3sqrt%285%29 is a root,
then 2-3sqrt%285%29 is also a root.  And since it has 3-2i as a root,
3+2i is also a root.  So if it were solved we would have to end up with
these four solutions:

x = 2+3sqrt%285%29, x = 2-3sqrt%285%29, x = 3-2i, x = 3+2i

So before that we would have had

x - (2+3sqrt%285%29) = 0, x - (2-3sqrt%285%29) = 0, x - (3-2i) = 0, x - (3+2i) = 0

And before that we would have had:

x - 2 - 3sqrt%285%29 = 0, x - 2 + 3sqrt%285%29 = 0, x - 3 + 2i = 0, x - 3 - 2i = 0

And before that we would have had:

(x - 2 - 3sqrt%285%29)(x - 2 + 3sqrt%285%29)(x - 3 + 2i)(x - 3 - 2i) = 0

Now we must multiply that out and collect terms to get our fourth
degree polynomial equation:

It will be easier if we group the first two terms in each parentheses:

[(x-2) - 3sqrt%285%29][(x-2) + 3sqrt%285%29][(x-3) + 2i][(x-3) - 2i] = 0

The first two bracket expressions are like multiplying (A+B)(A-B)=A²-B², and
the last two bracketed expressions are too:

[(x-2)² - 9·5][(x-3)² - 4i²] = 0

[(x-2)² - 45][(x-3)² - 4(-1)] = 0

[(x-2)² - 45][(x-3)² + 4] = 0

[x²-4x+4 - 45][x²-6x+9 + 4] = 0

(x² - 4x - 41)(x² - 6x + 13) = 0

x4 - 6x³ + 13x² - 4x³ + 24x² - 52x - 41x² + 246x - 533 = 0

x4 - 10x³ - 4x² + 194x - 533 = 0

Edwin