Positive SSL
    14.素養(4)
1 如圖所示電路,求Req 為多少? 109 統測
A 3R Ω
B (1+3 )R Ω
C 2R Ω
D (1+2)R Ω

如上圖所示,因為電路是無窮多,所以Req = Req1,電路化簡變成如下

設 Req = x  ∵ Req = Req1  ∴ Req1 = x

x = R + R⫽x + R

x = 2R + R.xR+x

x(R+x) = 2R(R+x) +R.x

x2 + R.x = 2R2 +2R.x+ R.x

x2 - (2R)x - 2R2 =0

x = 2R ± 4R2 + 8 R2 2  (-不合)

x = 2R + 12R2 2

x = R + 3R

x = (1 + 3)R