# Formula for resistance in parallel circuit

1. Apr 7, 2005

### DB

My science teacher gave me this formula for resistance in parallel circuit.
$$\frac{1}{R_{eq}}=\frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+.....$$

Thats exactly how he wrote it.
I would like this using the summation sigma

$$\frac{1}{R_{eq}}=\sum_{R=\frac{1}{R_n}}^n$$

Is that right? Im sure it's not lol....

2. Apr 7, 2005

### ZapperZ

Staff Emeritus
Not quite. You should write it as

$$\frac{1}{R_{eq}}=\sum_{i=1}}^n \frac{1}{R_i}$$

Zz.

3. Apr 7, 2005

### Crosson

$$\frac{1}{R_{eq}}=\sum_{i=1}^n \frac{1}{R_i}$$

Where n is the number of resistors and i is just a dummy letter (a counter).