As written, there is only one interpretation:
6/2(1+2) = 6/2*(1+2) = 3*(1+2) = 3*3 = 9
The shorthand notation 2(1+2) must always be remembered to be 2*(1+2) and, following the order of operations (PEMDAS), one does multiplications and divisions from left to right as they appear.
To get an answer of "1", one must write "6/(2(1+2))" or "6/(2*(1+2))" --- it is not arbitrary in Mathematics.