Question

Which of the following sets represents a function?

{(3, 5), (-1, 7), (3, 9)}
{(1, 2), (3, 2), (5, 7)}
{(1, 2), (1, 4), (1, 6)}

Answer 1

{(1, 2), (3, 2), (5, 7)} I think that is right.

Answer 2

The 1st set has 5 different values of +y+
for +x+=+1+ and violates definition
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The 2nd set is a function
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The 3rd set has

( 1,2 ) & ( 1,1 )
( 2,3 ) & ( 2,2 )
( 3,4 ) & ( 3,3 )
Each of these pairs violates the definition
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The 4th set has ( 2,-7 ) & ( 2,0 ) which
violate definition