Can't understand factorising by taking out common factorsWatch
I'm going to try explain it as simply as poss
With 3x-6, you split into 2 parts, "3x" and "-6" find a common factor (3) and factorise.
Do exactly the same with (2t+s)(2t-s)+(2t-s), split to get "(2t+s)(2t-s)" and "1 X (2t-s)", it is clear that (2t-s) is a factor you can take out of both, which leaves you with (2t+s) and 1, = 2t+s+1
ANSWER= Factor X what is left over
Remember t and a are just unknowns, so 2t+s as well as 2t-s are just numbers. So it may be like this where 2t+s=5 and 2t-s=3
Then you could expand if you want to, but I hope that illustrates my point that you just treat (2t+s) and (2t-s) like ordinary numbers, as after all that's what they are, but with unknowns in them which seem to make it look harder.