Answer:
x = 3/4 and x = -4/5
Explanation:
20x⁴ + x³ + 8x² + x − 12
Group:
(20x⁴ + 8x² − 12) + (x³ + x)
Factor:
4 (5x⁴ + 2x² − 3) + x (x² + 1)
4 (5x² − 3) (x² + 1) + x (x² + 1)
(x² + 1) (4 (5x² − 3) + x)
(x² + 1) (20x² + x − 12)
(x² + 1) (4x − 3) (5x + 4)
So the rational roots are x = 3/4 and x = -4/5.