∫dx/(x^4+1)=∫1/(x^4+1+2x^2-2x^2) dx=∫1/{(x^2+1)^2-2x^2} dx
=∫1/{(x^2+√2x+1)(x^2-√2x+1)} dx=(1/4)∫(√2x+2)/(x^2+√2x+1) + (2-√2x)/(x^2-√2x+1) dx
=(1/4)∫(√2x+1)/(x^2+√2x+1) + 1/(x^2+√2x+1) + (1-√2x)/(x^2-√2x+1) + 1/(x^2-√2x+1) dx
=(√2/4){(1/2)*log{(x^2+√2x+1)/(x^2-√2x+1)} + arctan{√2x/(1-x^2)}} + C