Question

If two resistors are connected in series their effective resistance is 9 ohm. When they are connected in parallel their effective resistance is 2 ohm. Find the individual resistance? ​

Answer 1

let the resistors be 'a' and 'b'

when in series,

  a+b=9  ⇒ b=9-a

when in parallel,

   1/2=1/a + 1/b

    1/2 = 1/a + 1/(9-a)

   1/2=(9-a+a)/a(9-a)

   18=9a-a²

    a²-9a+18=0

   ⇒a=6 or 3

  when a=6.

       b=9-6=3

when a=3,

       b=9-3=6

Answer 2

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