Final answer:
When rounding the calculated measurement of approximately 8.6 units to the nearest tenth, it remains unchanged at 8.6 units.
Step-by-step explanation:
If we calculate the measurement of the missing side of a right triangle using the Pythagorean Theorem and obtain a result of approximately 8.6 units, we need to round this to the nearest tenth. The options available are 8.6, 8.7, 8.5, and 9.0 units. Since the calculation has not indicated that it needs to be adjusted upward or downward, the nearest tenth to 8.6 units is exactly 8.6 units. Therefore, when rounding 8.6 to the nearest tenth, the correct measurement remains at 8.6 units.