∫[0,a]ln(x+√(a^2+x^2)dx
=xln(x+√(a^2+x^2))|[0,a] -∫[0,a]x[1+x/√(a^2+x^2)]dx/[x+√(a^2+x^2)]
=aln(a+√2a)-∫[0,a]xdx/√[a^2+x^2]
=aln(a+√2a)-√(a^2+x^2)|[0,a]
=aln(a+√2a)-√2a+a