Hello!
Interval notation is written using brackets or parentheses. Brackets mean that the value of the corresponding side is equal to the function. Parentheses are the opposite of brackets in this case, and it is not part of the equation.
I will post the graph of this equation below.
Therefore, the domain of this equation in interval notation is (-∞, 6/7).
Note that it is parentheses not brackets. The graph does not go past 6/7, and infinity is not a number, it is a concept.
