## Sunday, May 31, 2015

### Circle Sector and Segment

Circle Sector and Segment
 Slices There are two main "slices" of a circle: ·         The "pizza" slice is called a Sector. ·         And the slice made by a chord is called a Segment.

 SECTOR OF A CIRCLE
Common Sectors
The Quadrant and Semicircle are two special types of Sector:

Half a circle is

a
Semicircle.

Quarter of a circle is
a
Area of a Sector

 A circle has an angle of 2π and an Area of: πr2 A Sector with an angle of θ (instead of 2π) has an Area of: (θ/2π) × πr2 Which can be simplified to: (θ/2) × r2

Area of Sector = ½ × θ × r2   (when θ is in radians)
Area of Sector = ½ × (θ × π/180) × r2   (when θ is in degrees)

 Arc Length By the same reasoning, the arc length (of a Sector or Segment) is: L = θ × r   (when θ is in radians) L = (θ × π/180) × r   (when θ is in degrees)

 Area of Segment The Area of a Segment is the area of a sector minus the triangular piece (shown in light blue here). There is a lengthy reason, but the result is a slight modification of the Sector formula: Area of Segment = ½ × (θ - sin θ) × r2   (when θ is in radians) Area of Segment = ½ × ( (θ × π/180) - sin θ) × r2   (when θ is in degrees)

### ARC LENGTH, PARAMETRIC CURVES

ARC LENGTH, PARAMETRIC CURVES

Arc Length, Parametric Curves

Parametric Curves. A parametric curve can be thought
of as the trajectory of a point that moves trough the plane with coordinates
(x, y) = (f(t), g(t)), where f(t) and g(t) are functions of the
parameter t. For each value of t we get a point of the curve. Example:
A parametric equation for a circle of radius 1 and center (0, 0) is:
x = cos t, y = sin t .
The equations x = f(t), y = g(t) are called parametric equations.

Given a parametric curve, sometimes we can eliminate t and obtain
an equivalent non-parametric equation for the same curve. For instance
t can be eliminated from x = cos t, y = sin t by using the trigonometric
relation cos2 t + sin2 t = 1, which yields the (non-parametric) equation
for a circle of radius 1 and center (0, 0):
x2 + y2 = 1 .

Example: Find a non-parametric equation for the following parametric
curve:
x = t2 − 2t, y = t + 1 .
Answer: We eliminate t by isolating it from the second equation:
t = (y − 1) ,
and plugging it in the first equation:
x = (y − 1)2 − 2(y − 1) .
i.e.:
x = y2 − 4y + 3 ,
which is a parabola with horizontal axis.