y is constantly 0 because those absolute values are equal. That's because what's between the first pair of absolute value bars is -1 times what's between the second pair. So it's just equivalent to y = 0 for all values. It is not necessary to take those special cases indicated. You can show y = 0 for ALL values of x this way: y = |-2x+5| - |2x-5| y = |-1(2x-5)| - |2x-5| y = |-1||2x-5| - |2x-5| y = 1|2x-5| - |2x-5| y = |2x-5| - |2x-5| y = 0 Edwin