(i) (x + y) + z and x + (y + z)
The tree diagrams are
Subtraction is not associative and the expressions are not equal.
(ii) (p × q) × r and p × (q × r)
The tree diagram is
Multiplication is associative
∴ Both expressions are equal.
(iii) a – (b – c) and (a – b) – c
Their tree diagrams are
Subtraction is not associative
∴ Both expressions are not equal.