Some of these cannot be factored in the reals.

An easy trick when the has no numbers in front of it is to look at the factors of the last number, and see if any of their sums is the middle number. If the last number is negative, then you look at the differences of the positive factors. This is a bit confusing...

Some examples

14 = 1*14 or 2*7. Do any of these differences (the sign of the last number is negative) make 5? Yes,
so


Another one

3 is prime and positive, so you are looking at the sum of 1 and 3 to make -4. But -3*-1= 3, and -3-1=4, so


Unless I'm mistaken, only the first one cannot be factored in the reals.