# Thread: Simplifiying - problem with parentheses

1. ## Simplifiying - problem with parentheses

I'm trying to teach myself how to simplify expressions and I'm having trouble with these two:

1. x - 2(9 + 6x)
2. 2(x - y)

I have been told that the answers are:
1. -11x -18
2. 2x - 2y
... but I have no idea how to get those answers.

This is how I tried to simplify them:
1. x - 2(9) + x - 2(6x)
2. 2(x) + 2(-y)

I think that is not right, but I don't understand what I'm doing wrong. How do you simplify these?

Thanks for any help.

2. Originally Posted by b47
I'm trying to teach myself how to simplify expressions and I'm having trouble with these two:

1. x - 2(9 + 6x)
2. 2(x - y)

...
to #1.:

To be exact your term has to be written like this:

$\displaystyle x-2*(9+6x)$

If you multiply a sum (written in brackets) you must multply each summand by the leading factor:

$\displaystyle x-2*(9+6x) = x-2*9 - 2*(6x)$

You have to observe the sign rules when multiplying: If the signs of the factors are equal (+*+ or -*-) the the result is positive (+) else it is negative.
Since 9 and 6 (of 6x) are positive numbers the result becomes:

$\displaystyle x-2*9 - 2*(6x) = x-18-12x$

You only can collect like terms, in this case you can collect the xes:

$\displaystyle x-18-12x=-11x-18$

And now it's your turn to do the 2nd example.