Let's see,
1.(20 - 3)^2
(20 - 3)^2= 20 - 3 = 17 * 17 = 289
2.(20 - 3) (20 + 3)
(20 - 3) (20 + 3) = 20 -3 =17 , 20 + 3 = 23 , (17)*(23) = 391.
3.(20 - 9) (20 + 9)
(20 - 9) (20 + 9) = 20 - 9 = 11 , 20 + 9 = 29 , (11)*(29)= 319.
4.(20 + 3)^2
(20 + 3)^2= 20 + 3 = 23 * 23 = 529
Answer: #2, (20 - 3) (20 + 3)
