When two resistors are connected in series, the equivalent resistance is 100 O.

Question

When two resistors are connected in series, the equivalent resistance is 100 O. When they are connected in parallel, the equivalent resistance is 30 O. What are the resistances of the resistors. Pls Help!

Explanation / Answer

When R1 and R2 is in series we have R = R1 + R2 = 100 ohm ==> R2 = 100 - R1 ............1 When R1 and R2 are in parallel we have R ' = R1*R2 / R1+R2 = 30 ohm ==> R1*R2 = 3000 ohm^2 Therefore (R1 + R2)^2 = R1^2 + R2^2 + 2R1*R2 ==> R1^2 + R2^2 = 4000 ==> R1^2 + 10000 + R1^2 - 200R1 = 4000 ==> R1^2 -100R1 + 3000 = 0 Solve this you get R1 and then substitute in 1 you get R2. I hope this helps you.

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