# Can't understand factorising by taking out common factors

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#1
I can do the easier ones (e.g 3x-6) it's when I see questions such as (2t+s)(2t-s)+(2t-s) I just don't know how to do them!

Posted from TSR Mobile
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7 years ago
#2
(Original post by Crob11258)
I can do the easier ones (e.g 3x-6) it's when I see questions such as (2t+s)(2t-s)+(2t-s) I just don't know how to do them!

Posted from TSR Mobile
What do you find hard about the latter example?
0
7 years ago
#3
(Original post by Crob11258)
I can do the easier ones (e.g 3x-6) it's when I see questions such as (2t+s)(2t-s)+(2t-s) I just don't know how to do them!

Posted from TSR Mobile
The latter example is exactly the same as the first. Ask yourself what factors occupy both parts of the function and then take them out.
0
7 years ago
#4
(Original post by Crob11258)
when I see questions such as (2t+s)(2t-s)+(2t-s) I just don't know how to do them!
Just look at both terms and see what they have in common. In this case they both have a factor of (2t-s).

0
7 years ago
#5
[QUOTE=Crob11258;46680103]I can do the easier ones (e.g 3x-6) it's when I see questions such as (2t+s)(2t-s)+(2t-s) I just don't know how to do them!

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
=(2t-s)(2t+s+1)
0
7 years ago
#6
Maybe it helps if you view it like this.

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

(2t+s)(2t-s)+(2t-s)
=(5)(3)+3
=3(5+1)
=(2t-s)[(2t+s)+1]

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.
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