Since the only thing that changed was the grouping (the parentheses), but the 9, 5, and 2 are in the same order, this is the associative property of multiplication.
In the second line, you'd put 45 and then 90:
   [tex](9\cdot5)\cdot2 = 45\cdot2 = 90[/tex]
In the third line, you'd put 10 and then 90:
   [tex]9\cdot(5\cdot2) = 9\cdot10 = 90[/tex]
The idea here is that regrouping an expression where everything is multiplication will not change the final result. Â It changes the order of operations, since things in parentheses are done first, but not the final outcome.
