Parent Sine and Cosine Functions

One period of the parent sine function y = sin x. Note the graph starts in the middle and starts to head up to a peak.
One period of the function y = - sin x. Note the graph starts in the middle and starts to head down to a trough.
One period of the parent cosine function y = cos x. Note the graph starts at a peak and ends at a peak.
One period of the function y = - cos x. Note the graph starts at a trough and ends at a trough.
– Tim Brzezinski

Information: Parent Sine and Cosine Functions