6.1 INTRODUCTION:
An angle is formed when two rays originate from the same end point.
If two lines intersect each other then vertically opposite angles are equal.
An angle which measures
( a ) 0 to 900 — acute angle
( b ) exactly 900 — right angle
( c ) 900 to 1800 — obtuse angle
( d ) exactly 1800 — straight angle
( e ) 1800 to 3600 — reflex angle