Identify the graph as eidentify the graph as either y = cos x or y = sin x

From the graph at x = 0, y = 0

Check1:
y = cosx

0 = cos(0)
0 = 1

therefore, this is not the function

Check2:
y = sinx
0 = sin(0)
0 = 0

therefore, this is the function

Conclusion:

the function in the graph is y = sinx