1. ## Alegbraic Expressions

I am trying to get an understanding of how these expressions are understood.
I have an example that I am working on which I require to use Identities to find a value of X.

The closest example that I can find at the moment from books is this Nested Brackets example;

7(a - {4 - 5(b - 3a)}) = 7(a - {4 - 5b + 15a})

= 7(a - 4 + 5b - 15a)

= 7a - 28 + 35b - 105a

= 35b - 98a - 28

So in the above example if I had to work that out starting from the top left hand side, I would follow through as;

-5b then -5 x -3a = + 15a, so at this point I now have;

-5b + 15a

then I would say 7 x a = 7a, and then 7 x 4 = 28, therefore;

then 7 x 5 = 35b, then 7 x (-15a) = -105a

so;

7a - 28 + 35b - 105a = 35b - 98a - 28

The part I don't understand?

How does -5b become +5b, and how does +15a become -15a?

I don't understand it?

In general:
-(-a)=+a
-(+a)=-a

3. ## Re: Alegbraic Expressions

Not really I understand what you have written, but in the first two lines of my example the -5b has changed to +5b, and the +15a has become -15a, and based on the above I am not sure how?

4. ## Re: Alegbraic Expressions

The negative sign, same as -1 is multiplied through the brackets.

5. ## Re: Alegbraic Expressions

Originally Posted by pickslides
The negative sign, same as -1 is multiplied through the brackets.
So you are saying that what I thought was -{4} is actually -1(4){-5b} worked out as +5b

If as you say the minus on its own is actually -1 then yes I understand that now