Posted by Anonymous on .
Select the relation that is a function.
a.
{(21, 11), (21, 10), (21, 9), (21, 8)}
c.
{(6, 5), (3, 2), (10, 8), (3, 3)}
b.
{(2, 1),(5, 1), (16, 3), (3, 9)}
d.
{(5, 10), (3, 10), (3, 10), (4, 7)}

Math 
Steve,
hint: each element must have a single image.

Math 
Anon,
Just tell the answer

Math 
Anon,
cause i don't understand what you saying

Math 
Steve,
Note that in (a) (21,11) and (21,10) indicate that f(21) = 11 and f(21) = 10.
That can't be so, for a function.
In (c), we have f(3) = 2 and f(3) = 3
In (b) there is only one mapping for each element.
In (d) we have f(3)=10 and f(3)=10.
each element can have only one image under the mapping. That is, the relation maps the first value to the second value in each pair.
A value can only be mapped to a single image. Better study the chapter on relations, mapping, images, etc. and what makes a function more restrictive than just a general relation. 
Math 
Anon,
so b?

Math 
Steve,
That'd be my guess, unless you have b and c switched. They are listed out of order.