SOLUTION: I'm trying to help my daughter with her homework to no avail. Please help. 7y-x-1=y-(2x+1) Solve for y in terms of x. This is what we have got so far. 7y-y-x-1=y-y-(2x+1

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Question 25301: I'm trying to help my daughter with her homework to no avail. Please help.
7y-x-1=y-(2x+1)
Solve for y in terms of x.
This is what we have got so far.
7y-y-x-1=y-y-(2x+1)
6y-x-1=2x+1
6y-x-1-1=2x-1-1
6y-x=2x
6y-x-x=2x-x
6y=x
6y/6=x/6
y=1/6x
but the answer is supposed to be -1/6x. Where did I go wrong?
Answer by kev82(151) (Show Source):
You can put this solution on YOUR website!
Hi,
You've managed to lose a minus sign almost right at the start. They're pesky little things, and I'm always losing them. The trick of a good mathematician is to lose an even number of them :D
I'm happy with the first two lines:

Now concentrate on the minus sign in front of

Where did it go? I dunno. Either it was just a simple mistake and you're now ok, or you have problems expanding brackets. In case of the latter there are two things to remember.
1) You can always write minus something as minus one times something.
2) When expanding brackets you multiply the outside by everything on the inside, and sum.
Using these two rules you get
So the next line should be
You've gone a bit wrong later on as well, but I think that's because you were trying to get the right answer after your first mistake. Have another go at it and see how you get on. These rules for solving simple equtaions might help you.
1) Everything you do to one side of the equation you must do to the other
2) Add and Subtract are opposites (To undo a subtract, you add and vice-versa)
3) Multiplication and division are opposites - but be careful of zero.
Hope that helps,
BTW - it's really nice to see someone who posts working. Out of all the questions I've answered I think you're only the second or third person to do it.
Kev