26.
블록선도의 전달함수 $\frac{C(s)}{R(s)}$는?
①
$\frac{G_1(s)G_2(s)}{1 + G_1(s)G_2(s)G_3(s)}$
②
$\frac{G_1(s)G_2(s)}{1 + G_1(s) + G_1(s)G_2(s)G_3(s)}$
③
$\frac{G_1(s)G_2(s)}{1 + G_2(s) + G_1(s)G_2(s)G_3(s)}$
④
$\frac{G_1(s)G_2(s)}{1 + G_3(s) + G_1(s)G_2(s)G_3(s)}$