Find the derivative of f(x)=ln(x+x2+a2)f(x) = \ln(x + \sqrt{x^2+a^2})f(x)=ln(x+x2+a2).
1x2+a2\frac{1}{\sqrt{x^2+a^2}}x2+a21
1x2+a2\frac{1}{x^2+a^2}x2+a21
xx2+a2\frac{x}{\sqrt{x^2+a^2}}x2+a2x
ax2+a2\frac{a}{\sqrt{x^2+a^2}}x2+a2a