You can show that the resistance has changed by reading values of current and voltage from the graph.

Remember that we can calculate resistance (R) by using R = V÷I.

What is the resistance when V=1 and V=3?

Read off values: V=1, I=0.2 R = V÷I = 1÷0.2 = 5 ohm

V=3, I=0.4 R = V÷I = 3÷0.4 = 7.5 ohm

The resistance increases!

It's probably wise that you know how to do this!