Which of the lines below has a slope of zero?
2 answers:
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The subtraction sign in front of the second set of parenthesis changes the signs on the terms inside those parenthesis. So this could be rewritten as 
. None of the exponents on the x are the same, so we will just express it in terms of descending powers of x. 
. This is also the same as 
if you don't like to start with a negative. Either one is correct.