Hi, The origin of this question was contemplating how to express the impedance of an inductor as a function of frequency, for non sinusoidal voltage wave-forms such as triangle waves, but in particular rectangular pulse trains. So going back to basics, I watched this video: He derives the impedance of the inductor from v = L* di/dt where i = ejwt so v = L * d(ejwt)/dt = jwL* ejwt and so v/i = jwL which I don't like because it seems like it is putting the cart before the horse, because you can apply a voltage across an inductor, but it's the current which is the dependent variable. So I'd prefer to set v = ejwt so i = 1/L * ∫ v dt = 1/L * ∫ ejwt dt = 1/L * 1/jw * ejwt + Constant ∴ v / i = jwL - Constant My first question is, is there a reason why both methods are justified? I can see that the former is more simple because you don't have the 'constant'. Okay, back to the main question of this post, taking for example a triangle wave as the current: So say I only went to n degree of 1 for simplicity. Then this would be: V = Linductance * (d f(x)/dt) V = Linductance* 8/Pi^2 * Pi/Fourier_L * cos (pi*x / Fourier_L) so X_l = Linductance* 8/Pi^2 * Pi/Fourier_L * cos (pi*x / Fourier_L) / f(x) which would be very complicated... Am I thinking about this right?