what does it mean "the expression can be rewritten by writing subtraction as the addition of the opposite ?

Question

if 3x2-5y+2xy-x-7 do I change the + to - and the - to + I have never taken these courses before and my instructor explains it so fast I didn't understand ?

Answer 1

Katherine, Subtraction is just adding the opposite. For example, if I have 5 - 7, I could rewrite it as 5 + -7. This is simple algebra. For your problem, it can be rewritten as 3x2 + -5y + 2xy + -x + -7.

Answer 2

In abstract mathematics subtraction operation is replaced by addition og the opposite element. If "a" is the given element (let say - number), then "-a" is the opposite element. Opposite element is the one which is being added to "a" makes zero. It looks like to subtract the same number from itself: a - a = 0.

Thus, your expression can be rewritten in the following way:

                                                    3x^2 + (-5y) + 2xy +(-x) + (-7)                 that's it.