The first problem is that the area enclosed by f(x) and X axis is a positive number.

But for the integral of f(x), the upper part of the X axis is positive and the lower part is negative, so the absolute value should be added.

The second question, I integrand function is odd function, and the integral value is 0.

The part of J integrand that contains X is odd function, but it is followed by-1, and the integral value is negative (-2).

The first half of k integrand function is odd function, and the second half is even function, and the integer value is > 0.