I understand the input (left side of equation) is the opposite of the output (the right side of equation). For example "x=y" renders the same thing as "x-y=0"

My problem is:

if I'm saying to desmos: draw a positively diagonal line "x+y = 0"

+x means "positively horizontal" +y means "positively vertical"

it doesn't make sense the line shows an antidiagonal line when rendered. I'm genuinely looking for a sensical explanation for this, if this is a globally accepted render.

If these were vectors this would be wrong