The substitution method based on the fact that under a certain nice condition about and we have that \[\int f(g(x))g'(x)dx=\int f(u) du\] where . From the statement above, in many cases it is clear how to choose the , namely the inner function of the composition function. On the videos below we will discuss how to do integration by substitution. In particular we discuss how to select the right in many situations. On the third video we discuss two challenging problems that we solve by substitution method.