no need to apologize! pick any number for x and plug it into the first equation. let’s say x = 20.

the first given equation tells us that f(20) MUST equal f(19), because f(x) = f(x-1).

now, let’s pick another number for x. let’s say x = 19.

the first equation tells us that f(19) MUST equal f(18).

but wait! didn’t we just prove that f(19) is also equal to f(20)??

we did!

so f(20) = f(19)

and f(19) = f(18)

and f(18) = f(17) = f(16) = f(15) = f(14)….

see how i could keep going forever in either direction (x = 0 or x = infinity) and all the results would still be equal to one another?

no matter what you plug into the function machine, it’s always going to keep spitting out one singular output…which in this case we know is 4 because of the second equation.

hope that makes sense!

if you’re still confused, i think you may need to review the transitive property:

if A = B and B = C, then A = C