39.
그림의 블록선도에서 $C(s)/R(s)$ 을 구하면?
①
$\frac{G_1(s)+G_2(s)}{1+G_1(s)G_2(s)+G_3(s)G_4(s)}$
②
$\frac{G_1(s)G_2(s)}{1+G_1(s)G_2(s)G_3(s)G_4(s)}$
③
$\frac{G_3(s)G_4(s)}{1+G_1(s)G_2(s)G_3(s)G_4(s)}$
④
$\frac{G_1(s)G_2(s)}{1+G_1(s)G_2(s)+G_3(s)G_4(s)}$