Convert the fractions to a common denominator.

Since both sides are reciprocals (each divided is into owe), disregard the

reciprocal function.

The formula for equal resistors in parallel,

is a simplification

of the general formula for resistors in parallel.

There are other

simplifications of the general formula for resistors in parallel which can

be used to calculate the total or equivalent resistance in a parallel

circuit.

(a) *Reciprocal Method.*

This method is based upon taking the

reciprocal of each side of the equation. This presents the general formula

for resistors in parallel as:

This formula is used to solve for the equivalent resistance of a number of

unequal parallel resistors. You must find the lowest common denominator in

solving these problems.

Example: Three resistors are connected in parallel as shown in figure 51 (on

the following page). The resistor values are: R1 = 20 Ohms, R2 = 30 Ohms,

R3 = 40 Ohms.

Using the reciprocal method, what is the equivalent

resistance?