# Intergral problem solving

• December 11th 2009, 11:44 AM
mathcalculushelp
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?
• December 11th 2009, 11:52 AM
chisigma
What is the derivative of $1+t^{2}$?... the answer is also the solution of integral (Wink) ...

http://digilander.libero.it/luposabatini/notte1.jpg

Merry Christmas from Italy

$\chi$ $\sigma$
• December 11th 2009, 12:51 PM
mathcalculushelp
the derivative
the derivative is 2tdt .But I did this at the top and I end up with some other number.
• December 11th 2009, 01:56 PM
Defunkt
Well, what's $\int \frac{1}{x}dx$ ?