No 19 is not a factor of 36. Some factors of 36 are 1,2,3,4,6,9,12,18 and 36.
-36 and -5
The fact that (-6)*(-6) = 36, for example.
This is missing some crucial information, but let's pick a number. Assume the missing number is 36. Since 36 is a factor of 72, all the factors of 36 are factors of 72.
2 x 2 x 3 x 3 = 36
The factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, 36 No two of them add up to 23.
Factors of 36 are 1, 2, 3, 4, 6, 9, 12, 18, and 36. The factors of 72 are 1, 2, 3, 4, 6, 8, 9, 12, 18, 24, 36, and 72. All of the factors of 36 are also factors of 72.
-36 and -12
Since 36 is a factor of 72, the factors of 36 are included in the factors of 72.
Since 12 is a factor of 36, the factors of 12 are contained in the factors of 36.
Well, 18 and 3 (both factors of 36) add up to 21. As well, the factors 12 and 9 add up to 21.
All factors of 18 are factors of 36, because 18 itself is a factor of 36.