Showing $5a + 2b \equiv 0 \pmod 7$ is symmetric, pictorially I have a problem regarding the understanding of modulus.
So someone proved $5a + 2b \equiv 0\pmod 7$ is symmetric using the modulo circle,
and my brain cant comprehend how he meant that. I'm talking about circles like this:

I know there is a other way to prove it with $7 \mid 5a + 2b$

modular arithmetic is basically arithmetic done using linear polynomials:$$y\equiv c\bmod m\iff y=mx+c$$ for some integer values of x,m,c, and y. So it's basically saying, in this case that: $$5a+2b=7x$$ if we allow $a=b=x=n$ where n is integer, then we have a solution.  Edit more to the point $5=7+(-2)$ so if the original has an answer so will $-2a+2b=7x$
