What are the trigonometric ratios of any angle α?

The sine of α is the value of the ordinate of point P on the unit circle.
The cosine of α is the value of the abscissa of point P on the unit circle.
The tangent of α is the quotient of the ordinate by the abscissa of point P on the unit circle.
The sign of the trigonometric ratios depends on the quadrant where the second side of the angle falls.
If the second side of the angle coincides with an axis, then the angle has some null trigonometric ratio.