For the series combination of three resistors establish the relation :
` R=R_(1)+R_(2)+R_(3)`
where the symbols have their usual meanings.
Calculate the equivalent resistance of the combination of three resistors of `6Omega , 9 Omega` and `18 Omega` joined in parallel.

Explanation

To solve the problem, we will break it down into two parts:

1. Establishing the relation for equivalent resistance in a series combination of resistors.
2. Calculating the equivalent resistance for three resistors connected in parallel.

### Part 1: Establishing the Relation for Series Combination

**Step 1: Understanding Series Combination**
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