Final answer:
For two resistors combined in series, where R1 is much greater than R2, the total series resistance will be nearly equal to R1. In parallel, the total resistance will closely approximate R2, the smaller resistance.
Therefore, the answer to the question is: (a) R1 for series resistance, and (b) R2 for parallel resistance.
Step-by-step explanation:
When combining two resistors R1 and R2 in series, where R1 is significantly larger than R2 (R1 >> R2), the total series resistance can be represented by the sum of the two resistances.
However, because R1 is much greater than R2, the series resistance will be very nearly equal to R1 since the smaller resistance has a negligible effect on the total.
In the case of parallel resistance, when R1 is significantly larger than R2, the total parallel resistance will be dominated by the smaller resistor, and will therefore be very nearly equal to R2.
This is because in parallel circuits, the total resistance is found by the reciprocal of the sum of the reciprocals of each individual resistance, causing the smaller resistance to have a greater impact.
Therefore, the answer to the question is: (a) R1 for series resistance, and (b) R2 for parallel resistance.