By use of the Nyquist criterion, determine whether the closed-loop systems having the following open-loops transfer functions are stable or not. If not, how many closed-loop poles lie in the right half s-plane. a. GH(s) = (1+4s)/(s^2)(1+s)(1+2s) b. GH(s) = 1/(s(1+2s)(1+s)) c. GH(s) = 1/((s^2)+100)