Linear functions and graphs

Change one equation in this pair of simultaneous equations very slightly and there is a big change in the solution. Why?

Follow hints to investigate the matrix which gives a reflection of the plane in the line y=tanx. Show that the combination of two reflections in intersecting lines is a rotation.

Can you find sets of sloping lines that enclose a square?

Four vehicles travelled on a road. What can you deduce from the times that they met?