One can think of the graph of sine being the graph of cosine with a translation of π/2 units to the left. Hence, moving the graph of cosine π/2 (in radians) units to the right will match the graph up with the sine graph. Thus, cos(x - π/2) = cos(x - 90°) = sin(x).
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One can think of the graph of sine being the graph of cosine with a translation of π/2 units to the left. Hence, moving the graph of cosine π/2 (in radians) units to the right will match the graph up with the sine graph. Thus, cos(x - π/2) = cos(x - 90°) = sin(x).
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