A line is a geometrical figure which is formed by a point by moving it in a particular direction also in the opposite direction. The angle is the space which is formed between two intersecting lines. When two forces act on a body then we represent the forces using the directed line segments. Also, we need to know the angles made by the forces to know the resultant force. Similarly, we must know the angle between the horizontal and the hill to know the height of the hill. Similarly, we can provide many other examples as the applications of lines and angles.
Some basic definitions of lines and angles are listed below.
Line segment:
A line which ahs both starting and ending points is called a line segment.
Ray:
A line which has only starting point but no ending point is called a ray.
Straight line:
A line which has neither starting nor ending points is called a straight line.
Vertex and arms of the angle:
Two lines intersect to form an angle. Here, the two lines are called the arms of the angle thus formed and the point where the lines intersected is called the vertex of the angle.
Acute angle:
An angle which is less than 90 degrees is called an acute angle.
Obtuse angle:
An angle which is greater than 90 degrees is called an acute angle.
Right angle:
An angle which measures 90 degrees is called a right angle.
Straight angle:
An angle at any point on a straight lie measures 180 degrees which is called a straight angle.
Reflex angle:
An angle which is greater than 180 degrees and less than 360 degrees is called the reflex angle.
Supplementary angles:
Two angles which add upto 180 degrees are called supplementary angles.
Complementary angles:
Two angles which add up to 90 degrees are called complementary angles.
Adjacent angles:
Two angles are said to be adjacent if they share a common arm.
Linear pair of angles:
Two angles are said to form a linear pair if they are adjacent and supplementary.
Vertically opposite angles:
When two lines intersect each other then 4 angles are formed. Among them, two pairs of non – adjacent angles are called vertically opposite angles.
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