need help!!!

[nandip]

i need to simplify by combining like terms:
this is my problem:
-5x-7x
would the answer be 2x??

 

[mmm4444bot]

-5x-7x

would the answer be 2x ? Nope.

If we were adding 7x to -5x, then the result would be 2x.

-5x + 7x = 2x

That's because -5 + 7 = 2

BUT, we are not adding 7x, in this exercise.

We are subtracting 7x.

So, what is -5 minus 7 ?

Here's three different ways of looking at it:



Subtracting 7 is the same thing as adding -7:

-5x - 7x = (-5x) + (-7x)



Or, factor out the negatives:

-5x - 7x = -x(5 + 7)



Or, use a graphical interpretation, in your head:

If you're at -5 on the Real number line, and you move 7 units to the left (subtraction), where do you end up? That's how many x's there are.