examples: 2+7x+1-7x
9r+6-7
2x+x
8m-6m
-7x-7x
-8+5m=1=9m
HELP!!!
The method for these really aren't that hard, let's take one of your examples:
$\displaystyle 2 + 7x + 1 - 7x$
1. Split up all like terms
We can see that 2 and 1 are just regular numbers and that 7x and -7x have an x in common, so we will split them up that way, I like to use parentheses to avoid confusion:
$\displaystyle (2 + 1) + (7x - 7x)$
2. Solve the parentheses 1 by 1.
We can see that 2 + 1 is three, but the 7x - 7x is tricky. For a moment, let's pretend that there is not an x there, we would then have:
$\displaystyle 7 - 7$
This is obviously 0.
$\displaystyle 7 - 7 = 0$
Now, let's put the x back in, this time we multiply everything by x, even the zero, since they are like terms:
$\displaystyle 7x - 7x = 0x = 0$ (Zero times anything is zero)
And there you have it, we just put that where we put the (7x - 7x) in the problem:
$\displaystyle 3 + 0 = 3$
Hope this helps.