"use function notation to write the equation of the line:

"

I noticed that the value of x is equal to the value of y. When x is 1, y is also 1. Thus, y = x

The function notation of y = x is:

f(x) = x

f(x) represents the value of y in the function notation.

f(1) = 1       f(-1) = -1
f(2) = 2       f(-2) = -2
f(3) = 3       f(-3) = -3
f(4) = 4       f(-4) = -4
f(5) = 5       f(-5) = -5