(x + 1)(x - 1)(x + 5)(x - 3) is the fully factored form of the polynomial.
The zeros are (-1, 0), (1, 0), (-5, 0), and (3, 0).
x^4 + 2x^3 - 16x^2 - 2x + 15
We can use the rational roots theorem to find some of the possible roots, and after finding just one root, we can simplify this polynomial.
List factors of 15:
1, 3, 5, 15.
List factors of 1:
1.
Our possible rational factors are:
+/- 1, +/- 3, +/- 5, +/- 15.
To find factors, we can use the remainder theorem.
Replace all x values with 1.
1^4 + 2(1)^3 - 16(1)^2 - 2(1) + 15 = 0
Because the answer is zero, it means that 1 is a root.
We can divide this polynomial by x - 1 to find a simplified form.
After dividing, our quotient is: x^3 + 3x^2 - 13x - 15
We can continue finding factors by using the rational roots theorem. Once we have only three terms, we can try to factor using the AC method.
Our next possible root is -1.
(-1)^3 + 3(-1)^2 - 13(-1) - 15 = 0
We know that -1 is also a root, and so we can divide the polynomial by x + 1.
After diving we're left with x^2 + 2x - 15.
Now, we can try to factor using the AC method.
List factors of -15.
1 * -15
-1 * 15
3 * -5
-3 * 5 (these digits satisfy the criteria.)
Split the middle term.
x^2 - 3x + 5x - 15
Factor binomials.
x(x - 3) + 5(x - 3)
Rearrange binomials.
(x + 5)(x - 3)
Add in the two factors we already factored out.
(x - 1)(x + 1)(x + 5)(x - 3)
