∫(-1到1) dx/(x²+1)²= 2∫(0到1) dx/(x²+1)²令x=tanz,dx=sec²z dz当x=0,z=0 // 当x=1,z=π/4= 2∫(0到π/4) (sec²z)/(sec⁴z) dz= 2∫(0到π/4) cos²z dz= ∫(0到π/4) (1...