Write a mathematical proof of the algebraic equivalence of (pq)r and (qr)p

The answer 
equivalence of (pq)r and (qr)p

in mathematics,  A is equivalent to B  if
1)  A implies B and B implies A,
or  2)  A = B
one of these conditions must be proven to prove equivalence

(pq)r = (p x q) x r, by using associative property of the multiplication, 
 (p x q) x r = p x (q  x r ) 
therefore,
 (pq)r= (p x q) x r =  p x (q  x r )= (qr)p, that means  (pq)r  equivalent to (qr)p