Ic=(15-0.3)/3000=0.0049 (A)
Ib=0.0049/40=0.0001225 (A)
Irb=(9+0.7)/20000=0.000485(A)
Irx= 0.0001225+0.000485=0.0006075
Rx=(5-0.7)/Irx=7078.189 Ω≈7.08 KΩ
所以选 A
Ic=(15-0.3)/3000=0.0049 (A)
Ib=0.0049/40=0.0001225 (A)
Irb=(9+0.7)/20000=0.000485(A)
Irx= 0.0001225+0.000485=0.0006075
Rx=(5-0.7)/Irx=7078.189 Ω≈7.08 KΩ
所以选 A