Question:
the combined resistance of two resistore is 25ohm and if they were in parralel combination there resistance becomes 4ohm what are there indivisual resistance
Answer:
Given,
R1 + R2 = 25 ohms
Therefore, R2 = 25 – R1
1/R1 + 1/R2 = ¼
So, (R1+R2)/R1R2 = ¼
Or, R1R2/(R1+R2) = 4
Or, R1R2/25 = 4
So, R1R2 = 100
Or, R1 x (25-R1) = 100
So, 25R1 – R12 – 100 = 0
- R12 + 25 R1 – 100 = 0
- R12 + 20R1 + 5 R1 – 100 = 0
R1(20 – R1) x -5(20 – R1) = 0
So, (20 – R1) (R1 - 5) = 0
So, either R1 = 5 or 20 ohms
Likewise, R2 = 25 – R1
So, R2 = either 20 or 5 ohms
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