First let me say that this is my daughter's 7th grade algebra homework. 2nd let me say I am not looking for the answer. 3rd, I'm ashamed to be asking for help on 7th grade math. And 4th, I don't know how to enter actual math formulas in this textbox so I am resorting to coding
I do not understand the meaning of the comma in this problem:
$$-4c/ab-8c/ab,a,b\ne0$$
I believe that based on what I have read online, the , means AND. So reading that formula would be something like 4c/ab-8/ab where both a AND b are not zero. Is that correct?
The notation used in the problem formulation is somewhat sloppy, insofar as the slash is meant to encompass both $a$ and $b$, and the two commas have different meanings: $$-{4c\over ab}-{8c\over ab},\qquad a,b\ne0\ .$$ The first comma separates the technical assumptions from the expression that has to be simplified by the solver, whereas the second comma is shorthand for "$a\ne0$ and $b\ne0$".
Note that, e.g., Mathematica interprets $\>c/ab\>$ as ${\displaystyle{c\over a}}* b$.