Because the integral of Ex=xf(x) from negative infinity to 0 is negative (x; 0，f(x)>0)

The absolute values of the integral values in negative infinity and positive infinity are the same, and their signs are opposite, so the sum after integration, that is, the integral E(X) from negative infinity to positive infinity is 0, while the integral E|x|=|x|f(x) from negative infinity to positive infinity is positive, which is twice the integral from 0 to positive infinity, so it is expected to be equal to 2/2 under the root sign.