53. f={(-1,18), (-2,12), (0,4), (5,4), (-3,4)}

    Do you see this: (-2,12) ?    It exactly means that f(-2) = 12.

    Do you see this: (5,4) ?      It exactly means that f(5) = 4.


    
55. f={(-3/4,-1), (-2,4), (5,2), (8,10)}

    Do you see this: (-2,4) ?    It exactly means that f(-2) = 4.

    Do you see this: (5,2) ?     It exactly means that f(5) = 2.

It's so simple.

To find f(-2) in 53, you just look through

53. f={(-1,18), (-2,12), (0,4), (5,4), (-3,4)}

and find that -2 is the first number in (-2,12),

so f(-2) is 12, because 12 is the number right after -2 in (-2,12)

They say "-2 is the input and 12 is the output"


To find f(5) in 53, you just look through

53. f={(-1,18), (-2,12), (0,4), (5,4), (-3,4)}

and find that 5 is the first number in (5,4),

so f(5) is 4, because 4 is the number right after 5 in (5,4)

They say "5 is the input and 4 is the output"

-------------------------------------

To find f(-2) in 55, you just look through

55. f={(-3/4,-1), (-2,4), (5,2), (8,10)}

and find that -2 is the first number in (-2,4),

so f(-2) is 4, because 4 is the number right after -2 in (-2,4)

They say "-2 is the input and 4 is the output"
To find f(5) in 55, you just look through

55. f={(-3/4,-1), (-2,4), (5,2), (8,10)}

and find that 5 is the first number in (5,2),

so f(5) is 2, because 2 is the number right after 5 in (5,2)

They say "5 is the input and 2 is the output"

What could be easier than that?

Edwin