求导
\(ln (t + \sqrt{t^2 + 1})\) = f(t)
\(ln (t + \sqrt{t^2 + 1})\) = f(t) 求f'(t)
解原式 = \(\frac {1+ \frac{2t}{2 \sqrt{t^2 + 1}}}{t + \sqrt{t^2 + 1}} \)
= \(\frac {1}{\sqrt{1+t^2}}\)
\(ln (t + \sqrt{t^2 + 1})\) = f(t) 求f'(t)
解原式 = \(\frac {1+ \frac{2t}{2 \sqrt{t^2 + 1}}}{t + \sqrt{t^2 + 1}} \)
= \(\frac {1}{\sqrt{1+t^2}}\)