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in a subtraction problem with two numbers that have variables, does the subtraction sign go to the second number making it a negative number?

I have the math equation -9x - 13 - 9x = -31. please help.

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Andres F. | Great Mathematician & Best tutorGreat Mathematician & Best tutor
4.8 4.8 (88 lesson ratings) (88)


Step 1: Add the 13 to where is the -31 to leave the x's alone like this: -9x-9x=-31+13

Step 2: Remember that when subtracting to negative numbers that the first negative stays the same while the minus sign changes to addition. Then second number has it's own negative sign like this: (-9x)+(-9x).

Step 3: Add both sides: (-18x)= -18

Step 4: Divide the -18 from x and put it under the other -18 then you will find x. Enjoy                                                                                                            

Darin B. | Experienced English, Social Studies, and Math TutorExperienced English, Social Studies, and...

It may also be helpful to reorganize the problem. Because this equation only involves subtraction and addition, you can regroup the equation by like terms.

-9x -9x -13

Robert B. | Experienced (15+ years), Patient, Effective.Experienced (15+ years), Patient, Effect...
4.9 4.9 (302 lesson ratings) (302)

-9x - 13 - 9x is equivalent to -9x - 13 + (-9x).

Remember that subtracting a number is equivalent to adding its opposite. Put another way,

a - b = a + (-b).

I hope this helps, and if you need more explained, please feel free to ask. I or another tutor will be happy to assist you.


Christopher D. | Mathematician and ProgrammerMathematician and Programmer
4.9 4.9 (303 lesson ratings) (303)

Yes. I like to think of it as "the negative sign 'sticks' with the number that follows it." For example:

c - a + b - d   =   -a + b + c - d