I use both Dixon and Riley to study for economics however some of the graphs in the Riley textbook are pretty confusing and don't show up in the Dixon textbook, eg. inflationary/deflationary gap, fiscal policy and budget outcomes (which looks especially crazy). At school we use the Dixon textbook (with occasional Riley handouts) so my teacher hasn't mentioned these graphs so I was wondering if they could be tested on or are necessary in the HSC exam.
In regards to the graphs you actually need to know and understand required by the syllabus
Topic 1
Tariff, Subsidy and Quota Graphs
Topic 2
Demand and Supply graph for Exchange Rates, also know the fixed exchange rate graph
Topic 3
AD/AS model (simple one, not the keynesian one) - cost push and demand pull inflation graphs
Lorenz Curve
Social and Private Cost Externality Graph
Optional: Demand and Supply for Labour Graph (i've seen it tested in a multiple choice maybe once)
Philips Curve (again, multiple choice)
The rest in the dixon book is pretty much there to add depth to your essays