Impedance and Trig Functions

Thread Starter


Joined Mar 8, 2012

The value of impedance has two components; resistive and reactive. Which trig function do we use to find the reactance when impedance is given and which trig function do we use to find the resistance when impedance is given?


Tony D.


Joined Feb 24, 2006
You don't need to use trigonometric functions. If you have a complex number like a + jb then the real part, a, is the resistance, and the imaginary part b is the reactance.

Now if the complex number is specified in polar form as a magnitude, Z, and an angle θ, then you can compute the real and imaginary parts as follows:
Rich (BB code):
Resistance = a = Re(Z,θ) = Z*cos(θ)
Reactance  = b = Im(Z,θ) = Z*sin(θ)
The inverse transformations are
Rich (BB code):
Z = SQRT(a^2 + b^2)
θ = arctan(b/a) = tan^-1(b/a)