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Further, if a sine wave is shifted by +90 degrees (i.e., leading and to the left), it may also be referred to as a cosine wave. Thus (sin (2 pi ft + 90^{circ}) = cos (2 pi ft)). Finally, if a sine wave is shifted by −90 degrees (i.e., lagging and to the right), it may be referred to as a negative or inverted cosine wave.