Final answer:
In a series circuit represented by Ohm's law, the correct formulas to use are I = I1 = I2 = I3 for region X and Req = R1 + R2 + R3 for region Y, indicating that current remains constant through components and resistances are additive.
Step-by-step explanation:
Wendy is working with Ohm's law and electric circuits and needs to know which formulas apply to regions marked X and Y in her graphic organizer. Ohm's law describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit and is given by V = IR. When multiple resistors are present in a circuit, their total or equivalent resistance (Req) and the total current depend on whether they are arranged in series or parallel.
In a series circuit, the total current (I) remains the same through all the components, and the voltages across each component add up. Hence, I = I1 = I2 = I3 which would be the correct formula for region X. For region Y, in a series circuit, the equivalent resistance (Req) is simply the sum of all individual resistances, thus Req = R1 + R2 + R3 is the correct formula.
However, in a parallel circuit, the voltage across all components is the same and the currents through each component add up to the total current, which is represented by I = I1 + I2 + I3, but this does not apply to the original question.