The equation #xyz = 1500# can be thought of as a system of equations. This particular system has #3# unknowns and #1# equation. As a result of this, there is not enough information to determine the exact values of #x, y# and #z#.
Consider this (incorrect) argument. Let's suppose that #x = 1#, #y = 1# and #z = 1500#. Then #xyz = (1)(1)(1500) = 1500#. This satisfies our given equation, so these must be the values of our variables.
But this is incorrect, because if #x = 10#, #y = 10#, and #z = 15#, then #xyz = (10)(10)(15) = 1500#. This still satisfies our equation, but none of the variables have the same value as previously concluded.
In general, if you have #n# equations and #k# unknowns with #k > n#, then there is not a unique solution to the system.
