For the challenge x1,y1,x2,y2
val distance: Double = sqrt(dx * dx + dy * dy)
There is no way a student can be expected to solve this problem after reading Chapter 2 of the book.
Chapter 2 of the book says nothing about calculating coordinates using square roots. I think challenges like that are very a-motivational for students because you are setting us up for failure.
If I see more challenges like that in the future of the book I am just going to send it back to Amazon for a refund. Im talking about if I see more challenges that are impossible to solve because you do not present us with the prerequisite data. It is depressing to a student.