Resistors are components found on most circuit boards and in most electronic devices. Since resistors do not come in every size, they have to be arranged in various ways to get the needed resistance. When three resistors are in parallel, then the total resistance, RT , can be calculated using the equation 1/RT = 1/R1 = 1/R2 = 1/R3 , where each of the resistances is in ohms.
a) Determine an expression for the total resistance, RT .
b) Determine an expression for the total resistance if R1 = R2 = R3 .
c) Determine an expression for the total resistance if R1 = 2R2 = 6R3 .

First understand the difference between series and parallel resistance. What would be the total resistance of 2 x10 ohm resistors in series vs. parallel? Learn the formula and the question you asked is easy.

using the equation 1/RT = 1/R1 = 1/R2 = 1/R3 ,

Your formula is incorrect. This should be: 1/RT = 1/R1 + 1/R2 + 1/R3

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