1. **State the problem:** Factor the polynomial $$5x^5 - 20x^4 + 5x^3 + 50x^2 - 20x - 40$$.
2. **Factor out the greatest common factor (GCF):** Each term is divisible by 5, so factor out 5:
$$5(x^5 - 4x^4 + x^3 + 10x^2 - 4x - 8)$$
3. **Group terms to factor by grouping:** Group the terms as follows:
$$(x^5 - 4x^4 + x^3) + (10x^2 - 4x - 8)$$
4. **Factor each group:**
- From the first group, factor out $$x^3$$:
$$x^3(x^2 - 4x + 1)$$
- From the second group, factor out 2:
$$2(5x^2 - 2x - 4)$$
5. **Rewrite the expression:**
$$5[x^3(x^2 - 4x + 1) + 2(5x^2 - 2x - 4)]$$
6. **Check if further factoring or common factors exist:** The two terms inside the bracket do not share a common binomial factor, so try to factor the original polynomial differently.
7. **Try factoring the original polynomial by grouping differently:** Group as:
$$(5x^5 - 20x^4 + 5x^3) + (50x^2 - 20x - 40)$$
8. **Factor each group:**
- From the first group, factor out $$5x^3$$:
$$5x^3(x^2 - 4x + 1)$$
- From the second group, factor out 10:
$$10(5x^2 - 2x - 4)$$
9. **Rewrite:**
$$5x^3(x^2 - 4x + 1) + 10(5x^2 - 2x - 4)$$
10. **Try to factor the quadratic expressions:**
- Factor $$x^2 - 4x + 1$$ using the quadratic formula:
$$x = \frac{4 \pm \sqrt{16 - 4}}{2} = \frac{4 \pm \sqrt{12}}{2} = 2 \pm \sqrt{3}$$
So it factors as:
$$(x - (2 + \sqrt{3}))(x - (2 - \sqrt{3}))$$
- Factor $$5x^2 - 2x - 4$$:
Find two numbers that multiply to $$5 \times (-4) = -20$$ and add to $$-2$$: these are 2 and -10.
Rewrite:
$$5x^2 - 10x + 8x - 4 = 5x(x - 2) + 2(4x - 2)$$
This does not factor nicely, so use quadratic formula:
$$x = \frac{2 \pm \sqrt{4 + 80}}{10} = \frac{2 \pm \sqrt{84}}{10} = \frac{2 \pm 2\sqrt{21}}{10} = \frac{1 \pm \sqrt{21}}{5}$$
11. **Final factored form:**
$$5[x^3(x - (2 + \sqrt{3}))(x - (2 - \sqrt{3})) + 2(5x^2 - 2x - 4)]$$
Since the second quadratic does not factor nicely, the polynomial is factored as much as possible over the reals with radicals.
**Answer:**
$$5x^3(x - (2 + \sqrt{3}))(x - (2 - \sqrt{3})) + 10(5x^2 - 2x - 4)$$
Polynomial Factor
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