The sine function starts at 0, goes up to 1 at $\frac{\pi}{2}$, comes back to 0 at $\pi$, goes down to -1 at $\frac{3\pi}{2}$, and back to 0 at $2\pi$. The cosine function starts at 1, goes down to 0 at $\frac{\pi}{2}$, to -1 at $\pi$, back to 0 at
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