Across: the Cosine

The sine is the point's height. The cosine is the other coordinate, the across: how far the point is right or left of the centre. $\cos\left(\theta\right)$ is the adjacent side divided by the radius 1, so it is the point's x coordinate. Left of the y-axis, it is negative.

So the point at θ is ($\cos\left(\theta\right)$, $\sin\left(\theta\right)$). At 90° the point is straight up at (0, 1), so $\cos\left(90^{\circ}\right) = 0$. In a triangle a cosine is never negative. On the circle it can be.