What are all the rational roots of the polynomial f of x is equal to 20 x to the 4th power plus x cubed plus 8 x squared plus x minus 12 ?

The polynomial factors as (20x² + x − 12)(x² + 1). The first factor splits into (5x + 4)(4x − 3), giving roots x = −4/5 and x = 3/4. The factor x² + 1 has no rational roots, so the complete list of rational roots is −4/5 and 3/4, choice A.

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