In the experiment of measuring resistance RX by volt ampere method, we use the circuit as shown in the figure to measure. The measurement result is expressed by dividing the reading of voltmeter by the reading of ammeter. As electrical appliances, voltmeter and ammeter have resistance, which will cause experimental error. (1) before the power is turned on, the slide of sliding rheostat should___ (select "left end", "right end" or "any position"); (2) the measured value is higher than the true value___ (select "too large", "too small" or "same"); (3) if the readings of voltmeter and ammeter are u and I respectively, and their own resistances are RV and RA respectively, the more accurate expression of Rx is___ (mathematical expressions are expressed in known letters)

In the experiment of measuring resistance RX by volt ampere method, we use the circuit as shown in the figure to measure. The measurement result is expressed by dividing the reading of voltmeter by the reading of ammeter. As electrical appliances, voltmeter and ammeter have resistance, which will cause experimental error. (1) before the power is turned on, the slide of sliding rheostat should___ (select "left end", "right end" or "any position"); (2) the measured value is higher than the true value___ (select "too large", "too small" or "same"); (3) if the readings of voltmeter and ammeter are u and I respectively, and their own resistances are RV and RA respectively, the more accurate expression of Rx is___ (mathematical expressions are expressed in known letters)

(1) It can be seen from the figure that when the slide moves to the rightmost end, the resistance is the largest, so before the power is turned on, the slide of the sliding rheostat should be at the right end. (2) I = ur, r = UI, the voltage measured is the voltage at both ends of the resistance, and the ammeter measured is the current sum of the voltmeter and the resistance, so the current value is too large, and the resistance measured according to the formula is too small. (3) from (2) analysis, IX = I-IV = I- Urv so RX = UXIX = ui-iv = ui-urv = urvirv-u