60, 120, 180 and so on.
2 and 10
20
-12
(6 + √20) ≈ 10.472 and (6 - √20) ≈ 1.528
12
12, 24, 36
20
4 and 24 8 and 20 12 and 16
140, 280, 420, 560, 700
The greatest common factor of 12 and 20 is 4.
2,6
The multiples of 4 that are under 28 are 4, 8, 12, 16, 20, 24, 28