Hi.

I am having some problems getting how to figure out what to do when I need to plug a letter into the integral.

∫ 1/ x^2 from 0 to 1. I integrate and get -1/x and since we can´t use 0 put a instead : (-1/a -1). Why does this equal oo? Do I plug some number in for a? How does this work? Also, which number do I evaluate (stick into the integral) first? Why?

Another example would be ∫ 1/x from 0 to 1. That comes out to ln x . There we have the same problem as before. We use a letter instead of 0. What then? How is it evaluated? I don´t get what to do when I need to plug a letter into the integral? What does it mean when I end up with some a letter and a number when I am evaluating?

Thank you!