SOLUTION: Help!! Find the complex zeros of the polynomial function. Write f in factored form. f(x)=x^3-8x^2+29x-52

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Question 970244: Help!!
Find the complex zeros of the polynomial function. Write f in factored form.
f(x)=x^3-8x^2+29x-52

Found 3 solutions by Alan3354, AnlytcPhil, MathLover1:
Answer by Alan3354(69443) About Me  (Show Source):
You can put this solution on YOUR website!

Find the complex zeros of the polynomial function. Write f in factored form.
f(x)=x^3-8x^2+29x-52
===================
If you find a real zero first, eg z, then divide by (x-z).
That will leave a quadratic equation.
-------
Try the factors of 52.
1, 2, 4, & 13 (plus and minus)
f(x)=x^3-8x^2+29x-52
f(1) = 1 - 8 + 29 - 52 = -30 not a zero
etc

Answer by AnlytcPhil(1806) About Me  (Show Source):
You can put this solution on YOUR website!
Find the complex zeros of the polynomial function. Write f in factored form.
f(x)=x^3-8x^2+29x-52
f%28x%29+=+x%5E3-8x%5E2%2B29x-52

First we try to find any real rational zeros.

The only possible rational zeros are ± the factors of 52. They are
±1, ±2, ±4, ±13, ±26, ±52

Try 1 using synthetic division

1 | 1 -8 29 -52
  |    1 -7  22
    1 -7 22 -30   Nope. f(1)=-30, not 0.


Try -1 using synthetic division

-1 | 1 -8 29 -52
   |   -1  9 -38
     1 -9 38 -90   Nope. f(-1)=-90, not 0.


Try 4 using synthetic division

4 | 1 -8  29 -52
  |    4 -16  52
    1 -4  13   0   Yes! f(4)=0.

That means (x-4) is a factor of f(x), and the quotient is
1x²-4x+13 (the numbers left of the 0 in the synthetic division.
So we have this factorization of f(x)

f(x) = (x-4)(x²-4x+13)   <-- that's the simplest factored form without 
                             using complex numbers!

We set that = 0
       (x-4)(x²-4x+13) = 0
        
     x-4=0;  x²-4x+13 = 0
       x=4      
             x+=+%28-b+%2B-+sqrt%28+b%5E2-4ac+%29%29%2F%282a%29+
             x+=+%28-%28-4%29+%2B-+sqrt%28%28-4%29%5E2-4%2A1%2A13+%29%29%2F%282%2A1%29+ 
             x+=+%284+%2B-+sqrt%2816-52%29%29%2F2+
             x+=+%284+%2B-+sqrt%28-36%29%29%2F2+
             x+=+%284+%2B-+6i%29%2F2
             x+=+%282%282+%2B-+3i%29%29%2F2
             x=%28cross%282%29%282+%2B-+3i%29%29%2Fcross%282%29
             x=2+%2B-+3i

So f(x) has real zero 4, and complex zeros 2+3i and 2-3i.

So allowing complex numbers we can find another factored form
for f(x) of only linear factors:

f(x) = (x-4)[x-(2+3i)][x-(2-3i)]

f(x) = (x-4)(x-2-3i)(x-2+3i) 
  
Edwin

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

f%28x%29=x%5E3-8x%5E2%2B29x-52......write -8x%5E2 as -4x%5E2-4x%5E2 and 29x as 13x%2B16x
f%28x%29=x%5E3-4x%5E2%2B13x-4x%5E2%2B16x-52....group
f%28x%29=%28x%5E3-4x%5E2%29-%284x%5E2-16x%29%2B%2813x-52%29
f%28x%29=x%5E2%28x-4%29-4x%28x-4%29%2B13%28x-4%29
f%28x%29=%28x-4%29%28x%5E2-4x%2B13%29....set f%28x%29=0
0=%28x-4%29%28x%5E2-4x%2B13%29
one real solution is: if 0=%28x-4%29 =>x=4
use quadratic formula to find other zeros:
%28x%5E2-4x%2B13%29=0
x+=+%28-b+%2B-+sqrt%28+b%5E2-4%2Aa%2Ac+%29%29%2F%282%2Aa%29+
x+=+%28-%28-4%29+%2B-+sqrt%28+%28-4%29%5E2-4%2A1%2A13+%29%29%2F%282%2A1%29+
x+=+%284+%2B-+sqrt%28+16-52+%29%29%2F2+
x+=+%284+%2B-+sqrt%28+-36+%29%29%2F2+
x+=+%284+%2B-+6i%29%2F2+....simplify
x+=+%28cross%284%292+%2B-+cross%286%293i%29%2Fcross%282%291+
x+=+%282+%2B-+3i%29+
so, complex solutions are:
x+=+2+%2B+3i+
x+=+2+-+3i+