Why is zero excluded from the domain and the range​

Create a real-life situation and create a system and show how it might be modeled algebraically with a system of equations (or inequalities) show all work include a few sentences explaining the situation, your variables of choice and what each represents, and how you would set it up and solve it algebraically. !

If 1/√5+1/√5+1=p+q√r , find the values of p, q and r

What is negative 3/9 times negative 2/8 ?