|Finding the Rule from Images|
In the graph above, the red curve is y = sin x. The blue curve is y = cos x.
Note that the value of cos x can be found by phase shifting the y = sin x curve o/2 units left.
Since is ¼ the period, to assign a cosine rule to a sine function, we simply phase shift
the sine curve ¼ the period to the left.
Example: if the period is , we perform a phase shift (h + ), then call it cosine.
In the diagrams, you see four sinusoidal curves. Find a sine function rule for each
then perform the correct phase shift to get 4 cosine function rules for the same curves.
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