How to define a tangent line; how to determine the angle a radius to a tangent forms.
How to find the angle of inclination of a line.
How to define the tangent function for all angles.
How to evaluate the tangent of 3*pi/4.
How to define and label a line segment.
How to construct a perpendicular line at a point on a line.
How to mark parallel lines, how to show lines are parallel, and how to compare skew and parallel lines.
How to find the length of tangent segments drawn to a circle from the same point.
How to identify parallel lines, a line parallel to a plane, and two parallel planes.
How to use standard form of a line.
How to restrict the domain of tangent so it will have an inverse function.
How to take the converse of the parallel lines theorem.