Careful, you are mixing apples and oranges. The max(min) will be the value of Y which is bigger(smaller) than every other value of Y for some region around your max(min) value.
Not X like you said, X is the input variable that determines your Y.
You should try graphing ax^2 + bx + c for...
the way i translated it was "if the area of the smallest big rectangle is not equal to the area of the biggest small rectangle, then the function is not Riemann integrable"