can you make notes about the important parts about this?

Trigonometry (which means "triangle measurement") is a branch of mathematics which is
concerned with the properties and applications of the (six) circular or trigonometric functions.
A Cartesian Coordinate System (named after the French philosopher and mathematician,
Rene Descartes (1596 – 1650) is formed in a plane by two perpendicular number (or real)
lines that intersect at the point corresponding to the number zero on each line.
Distance Formula. The undirected distance between any two points in the plane P1
(x1, y1
)

and P2
(x2, y2
), or the line segment P1P2 is:
d = |P1P2
| = √(x2 − x1
)
2 + (y2 − y1
)
2

The radius vector, r, is the length of the line segment from the origin to any given point
P (x1, y1
). Applying distance formula: r = √x
2 + y
2.

An angle is formed by 2 rays that have a common end point. This common endpoint is
called the vertex of the angle, and the rays are called the sides of the angle.
A positive angle is formed when rotation of the ray is in a counterclockwise direction, while
a negative angle is formed when rotation is in a clockwise direction.
An angle is said to be in standard position when a Cartesian coordinate system is
superimposed so that the vertex is at the origin and the initial side is along the positive axis.
If the terminal side coincides with one of the axes, the angle is a quadrantal angle.
Furthermore, angles that are in standard position and have the same terminal sides are
coterminal angles.
The reference angle (also called related) of a given angle is the acute angle formed by the
terminal side of the angle and the x-axis.
The radian is the angle measured by a circular arc whose length is equal to the radius of the
circle.
An angle with its vertex at the center of a circle is called a central angle and the segment of
the circle it intercepts is called the intercepted arc. The length of the intercepted arc is
called the arc length on the circular distance and the area bounded by the 2 sides of the
central angle and its intercepted arc is called a sector. The sector area and the arc length
are proportional to their central angles. Thus, when the radius of the circle and the central
angle are known, it is possible to compute the arc length (S) and the sector area (As
).

S = rθ
As =
1
2
r
2θ

where θ is in radian measure.
Linear velocity, v, is defined as the rate of change of linear displacement, s, with respect to
time, t, and for motion in a straight line, v = st. The unit of linear velocity is meters per
second.