Q: Evaluate where is the arc of the curve from the point to the point .

A: We know that the integral is exact, meaning that we can choose any path from to . In the solutions they have gone through the origin, along the coordinate axes. So the path taken is from to , and then to

The answers then state that:

The integral is then

Not sure how they get this? It looks like they've just subbed and into the first and second bit of the original integral?

I know it's going to be something obvious but I'd appreciate it if someone could help me out with this.

Thanks in advance

Craig