Question

Two rasistances when connected in parallel give resulttant value of 2 ohm; when connected in series the value become 9 ohm.
Calculate the value of each rasistance.

Answer 1

Let one resistance be x and the other be y

1/x+1/y=1/Rp

Rp=xy/x+y

2=xy/x+y

2x+2y=xy....(i)

x+y=Rs

x+y=9

y=9-x

Substituting this in (i)

2x+2(9-x)=(9-x)x

By solving it we get...

x²-9x+18=0

Solving the quadratic equation...

x=3. Or. x=6

y=6. y=3

Answer 2

Let 1 resistance ne x and other ne y

Then

1/x + 1/y = 1/2

y + x / xy = 1/2

x+y=9

So

9/xy=1/2

Xy = 18

And x = 9-y

So eq will form aa follows

Y square -9y+18=0

And ans is 6&3