Answer: (4)
s = np
\(\begin{array}{l}R_{1}+R_{2}=n\left [ \frac{R_{1}R_{2}}{R_{1}+R_{2}} \right ]\end{array} \)
R12+ R22+ 2R1R2 = nR1R2
R12+(2–n)R1R2 +R12 = 0
(Considering this quadratic equation, for real roots)
b2 – 4ac≥0
[(2–n)R2]2 – 4×1×R22 = 0(2–n)2R22 = 4R22
2-n = ±2
So n = 4