Main Question or Discussion Point
How do I evaluate the integral [tex]\int_a^b[/tex] f(x4) dx = [tex]\int_y^z[/tex] f(u) dx/du du, where u=x4
You are too harsh. Sure, for this function there are easy ways to do the integral. But for other functions f maybe you really should do the substitution. And why not learn to do the substitution on simple problems that can be evaluated in other ways? Then, for example, you can check your answers and see when you make a mistake.Why would you use that method to evaluate the integral? The integral you have posted can easily be evaluated using the power rule for integration.