### Trigonometric Remarks

T1.
The slope of a line is the tangent of the angle which the line makes
with the x-axis. Any of the six trigonometric funtions can be used to
express all of the others. If the tangent of the angle is m, then

The reason that the tangent is not used as a basis for the other
trigonometric functions is because the tangent has an infinite value
for a vertical line. The sine and cosine do not have that problem, so
they are used more commonly. For our purposes, the tangent will crop
up more commonly.

In this theorem, note that the formula for the secant appears.
That is because the slope distance is the horizontal distance times
the secant which we see.

T2.
The perpendicular distance between the two lines is the distance
between the y intercepts times the sine of the angle which the line
makes with the y axis which is the cosine of the angle it makes with
the x axis.