Question 183890
Do you mean the opposite of 5x^2-3x+7?  By that you probably mean 
-(5x^2 -3x + 7).  It may help to think of this as 
-1*(5x^2-3x+7), which would be according to the Distributive Property
-1*5x^2 + -1*(-3x) + -1*7
-5x^2 + 3x -7


If you ADD the original number plus its opposite, then you get zero.  I think the problem was to find the opposite.


R^2