第九题原式＝x{ln[x+√(1+x^2)]}^2-2∫ln[x+√(x^2+1)]d[√(1+x^2)]＝x{ln[x+√(1+x^2)]}^2-2√(1+x^2)ln[x+√(1+x^2)]+2x+C
