A distorted sinusoid has the amplitudes $\mathrm{A}_{1}, \mathrm{A}_{2}, \text{A}_3 \ldots \ldots$ of the fundamental, second harmonic, third harmonic, ...... respectively. The total harmonic distortion is
- $\frac{\mathrm{A}_2+\mathrm{A}_3+\ldots}{\mathrm{A}_1}$
- $\frac{\sqrt{\mathrm{A}_2^2+\mathrm{A}_3^2+\ldots}}{\mathrm{A}_1}$
- $\frac{\sqrt{\mathrm{A}_2^2+\mathrm{A}_3^2+\ldots}}{\sqrt{\mathrm{A}_1^2+\mathrm{A}_2^2+\mathrm{A}_3^2+\ldots }}$
- $\left(\frac{\mathrm{A}_2^2+\mathrm{A}_3^2+\ldots}{\mathrm{A}_1}\right)$