Refer to the attachment: For the part that is underlined in red, on the right hand side of the equation why does the integral's limits go from -5 to 100 + 100 to 12? It isnt going in sequence (due to the 100 to 12) and that doesnt make sense
Because it is given in the question.
We are told
Which is the same thing as saying
Going back to the question we want
Well...we know the value from -5 to 100, so lets use that. But to make this equal, we then need to go from 100 to 12! Therefore, we get
We already know but we don't quite know the integral of 100 to 12...so let's break that guy up in the same way.
Of course by reversing the limits we can find a numerical value.
To re-state...we choose our limits given the definitions in the original question