X and Y are natural numbers.

X = 1; Y = 1

X = 2; Y = 2

X = 3; Y = 3

X = 4; Y = 4

X = 5; Y = 3

X = 6; Y = 2

X = 7; Y = 1

X = 8; Y = 0

How do I express this with a formula? Please, help me!

Could it be this?

y = - | x - 4 | + 4 , where x is an integer in the interval [1, 8]

I don't know that this can be expressed as a single function....but....as a piecewise "function" we might try this

y = x 1 ≤ x ≤ 4 where x is an integer

y = -x + 8 5 ≤ x ≤ 8 where x is an integer

How do I express this with a formula?

\(\begin{array}{|rcll|} \hline Y = \min(X,8-X) \\ \hline \end{array}\)