x在(0,1)1/(1+x^2)≤ 1/(1+x^4) ≤ 1∫(0->1) dx/(1+x^2) ≤ ∫(0->1) dx/(1+x^4) ≤ ∫(0->1) dxπ/4 ≤ ∫(0->1) dx/(1+x^4) ≤ 1
