f(-x) = ∫<0, (-x)^2> (2-t)e^(-t)dt = ∫<0, x^2>(2-t)e^(-t)dt = f(x),则 f(x) 是偶函数。f(∞) = limf(x) = ∫<0, +∞>(2-t)e^(-t)dt= ∫<0, +∞>(t-2)de^(-t) = [(t-2)/e^t]<0, +∞> - ∫<0, +∞>e^(-t)dt= lim(t-2)/e^t + 2 + [e^(-t)]<0, +∞>= lim1/e^t + 2 + 0 - 1 = 1
