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This figure consists of two line graphs, labelled A and B, showing sinusoids out of phase with each other. The X or horizontal axes are labelled as time. The Y or vertical axes are labelled as voltage.

Graph A shows a sinusoidal waveform starting at the origin. It rises smoothly to a rounded peak. The line then drops smoothly down to a rounded trough the same distance below the X axis as the peak is above. Then it rises again to the next peak, which is the same height as the previous peak, and then drops again to a trough of the same depth. Several cycles are shown. The waveform is labelled I.

Graph B shows the waveform starting above the origin, at maximum voltage. It falls smoothly to a rounded trough. The line then rises smoothly to a rounded peak the same distance above the X axis as the trough is below. Then it falls again to the next trough, which is the same depth as the previous trough. Several cycles are shown. The waveform is labelled Q.

 1.7 Quadrature amplitude modulation (QAM)