# Math Help - Intergral problem solving

1. ## Intergral problem solving

Can somebody help me integrate
r(t)=t/1+t^2

I use the substitution method

t(1+t^2)^-1

let 1+t^2=u
2tdt=du
dt=du/2t

hence putting in ques

r(t)=∫t/u^-1 du/2t
=1/2∫u^-1 du
=1/2u^0/0

which is not possible .Any help?

2. What is the derivative of $1+t^{2}$?... the answer is also the solution of integral ...

Merry Christmas from Italy

$\chi$ $\sigma$

3. ## the derivative

the derivative is 2tdt .But I did this at the top and I end up with some other number.

4. Well, what's $\int \frac{1}{x}dx$ ?