4. (20 pts) Find the length of the cardioid r = a(1 - cos θ), as shown in Fig 2.
Fig. 2. The cardioid r = a(1 - cos θ).
49. 控制系統補償器如圖(十八)所示,為何種補償器及其轉移函數為何?
(A) 領先補償器,(R2+1 /SC)/(R1+R2+1/SC)
(B) 落後補償器,(R1+1 /SC)/(R2+1/SC)
(C) 領先補償器,( 1 /R1+SC)/( 1/R1+1/R2+SC)
(D) 落後補償器,(SC+R2 )/(R1+R2+SC)