Subtraction in Lesson 32 is tricky. Example: 4 1/4 – 2 3/4 You cannot subtract 3/4 from 1/4. You must borrow 1 whole from the 4.
Lucas stopped. His pencil hovered over the paper. 90 degrees counterclockwise. He knew the rule in his head: swap the x and y, and change the sign of the new x. But looking at the rectangle on the graph, it looked wrong in his mind's eye. If he turned it, would it overlap the original? Would it go off the grid?