hi, attached are my working. Pls verify if my answer were correct. first convert norton part to thevenin. thus the current-ctrl voltage source is 70i & 20Ω in series with the circuit. to compute V, -10 + 10i + 20i - 70i=0 i= -0.25A i(20)-(70i)= -5+17.5= 12.5V =V next to compute I short the ab terminal, I= i - 3.5i v=0, (-10+v)/10 = -i i= 1 thus, I= 1 - 3.5 = -2.5A hence R= 12.5/-2.5 = -5Ω i m wondering if i got them right.
To my knowledge you can't have negative resistance.. so maybe your current shoudlnt be negative because I'm pretty sure you got your voltage correctly
remove the load, parallel the resistors until you get a simple series cct, reinsert the load and then calculate....no?