Question

Determine whether the formula describes y as a function. Explain your reasoning.

y = 9x + 1

Answer 1

do you know that if you have
y = mx + b
then you have the equation of a line ?

y= 9x+1
is the equation of a line
for every x, there is exactly one 1. This makes it a function

Answer 2

In addition to great comment from @phi , that formula will pass the "vertical line test" when drawn on Cartesian plane, thus making it a function.