Two ammeters, 1 and 2 have different internal resistances: `r_(1)` (known) and `r_(2)` (known). Each ammeter has scale such that the angular deviation of the needle for zero is proportional to the current passing through it. Initially, the ammeters are connected in series to a source of constant voltage. The deviations of the needles of the ammeter are `theta_(1)` and `theta_(2)`, respecitively. The ammeters are then connected in parallel ot the same voltage source. This time, the deviations of the needles are `theta'_(1)` and `theta'_(2)` respectively. Find `r_(2)` in terms of `r_(1), theta_(1), theta_(2), theta'_(1)` and `theta'_(2)`.