Examples 1.2.7(a):
If the graph of a function is known, how can you decide whether a function is
one-to-one (injective) or onto (surjective) ?
Injection
If a horizontal line intersects the graph of a function in more than one place, then there are two different points a and b for which f(a) = f(b), but a # b. Then the function is not one-to-one.-
Not a one-to-one function
Surjection
If you place a light on the left and on the right hand side of the coordinate system, then the shadow of the graph on the y axis is the image of the domain of the function. If that shadow covers the range of the function, then the function is onto.-
Not an onto function
(if range is R)