2. A Formula or an equation can be used

   Let a = { 1, 2, 3 } and B = { 5, 7, 8 } Note that f ( 1 ) = 2 ( 1 ) + 3 = 5
   f ( 2 ) = 2 ( 2 ) + 3 = 7 and
   f ( 3 ) = 2 ( 3 ) + 3 = 9
   i.e. f ( x ) = 2 x + 3 where x Î A and f ( x ) Î B.
   This is the formula which exhibits the function 'f'

3. Graphs can be used.

   Click here to enlarge

   Note that a vertical line parallel to y-axis, intersects the graph at one and only one point.

4. A table may be used. Consider y = 2x + 3 then,

Types of Functions

1. One - One ( 1 - 1 ) Function

   A function f : A ® B is one-one if different elements of A have different images in B. It is also called 'injection'.

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