Answer: x = {-3, -1, 1, 7}
Step-by-step explanation:
f(x) = x⁴ - 4x³ - 22x² + 4x + 21
possible roots are: +/- 1, 3, 7, 21
Let's try x = 1
1 | 1 -4 -22 4 21
| ↓ 1 -3 -25 -21
1 -3 -25 -21 0 remainder is 0 so (x - 1) is a factor
(x - 1)(x³ - 3x² - 25x - 21)
Next, let's try x = -1
-1 | 1 -3 -25 -21
| ↓ -1 4 21
1 -4 -21 0 remainder is 0 so (x + 1) is a factor
(x - 1)(x + 1)(x² - 4x - 21)
Then, factor the third polynomial
(x - 1)(x + 1)(x + 3)(x - 7)
Now, set each factor equal to zero and solve each one.
(x - 1) = 0 ⇒ x = 1
(x + 1) = 0 ⇒ x = -1
(x + 3) = 0 ⇒ x = -3
(x - 7) = 0 ⇒ x = 7
