The V-i graph for a conductor makes an angle θ with V-axis. Here V denotes the voltage and i denotes current. The resistance of conductor is given by
(4) At an instant approach the student will choose tanθ will be the right answer. But it is to be seen here the curve makes the angle θ with the V-axis. So it makes an angle (90 – θ) with the i-axis.
So resistance = slope = tan (90 – θ) = cotθ.