Answer:
(x-2), (x+2), (3x-5)
Explanation:
Factors of 3: ±1, ±3
Factors of 20: ±1, ±2, ±4, ±5, ±10, ±20
Possible factors of the polynomial: ±1, ±2, ±3, ±4, ±5, ±10, ±20, .... (there's a lot more but you probably do not need to list them all)
Pick a number to divide the polynomial by (I picked 2)
(3x³-5x²-12x+20)÷(x-2) = 3x²+x-10
So (x-2) is a factor of f(x) = 3x³-5x²-12x+20
Factor 3x²+x-10 = (3x-5)(x-2) these are the other factors of f(x) = 3x³-5x²-12x+20