# 7 Maths 5 lines and angles part 1

## Introduction

**Line**

A line is infinite and straight. A line is a *set* of continuous points that extend
indefintely in either of its direction

**Line Segment
**A line segment is a straight line segment which is part of the
straight line between two points. To identify a line segment, one can
write AB or .
The points on each side of the line segment are referred to as the end points.

** **

**Ray
**A ray is the part of the line which consists of the given point
and the set of all points on one side of the end point.

A is the end point and this ray means that all points starting from A are included in in the ray. A ray can also be written like:

(Source- mrudula, 4-6-13 , Lines, Ray and Line Segments)

## Angle

An **angle **is formed when two rays (*AB *and *AT*)
share a **vertex **(point *A*).

• The two rays are the sides of the angle.

• The interior of an angle is the set of all points between the sides of the angle.

• The exterior is the set of all points outside the angle.

Exercise : * *http://www.ck12.org/geometry/Congruent-Angles-and-Angle-Bisectors/exerciseint/Angles-and-Algebra/

Exercise : http://www.ck12.org/geometry/Congruent-Angles-and-Angle-Bisectors/exerciseint/Total-Angle/

## Types of Angles

Angles can be grouped into four different categories.

**Straight
Angle:** An
angle that measures exactly 180 deg.

**Acute
Angles:** Angles
that measure between 0 deg and
up to but not including 90 deg.

**Obtuse
Angles:** Angles
that measure more than 90 deg but
less than 180 deg.

** **

**Right
Angle:** An
angle that measures exactly 90 deg.

This
half-square marks right, or 90 deg, angles. When two lines intersect to
form four right angles, the lines are **perpendicular.**

Even though all four angles are 90 deg only one needs to be marked with the half-square.

(source- mrudula, 13-6-13, Lines and Angles)

#### Example A

What type of angle is 84 deg?

84 deg is
less than 90 deg, so
it is **acute**.

(source- mrudula, 13-6-13, Lines and Angles)

## Related Angles:

### Complementary Angles:

Two angles are **complementary** if
they add up to 90 deg. Complementary angles **do not** have
to be *congruent* or *next to each other*.