

Yes, it is. The division of a by b in the set of real numbers and the set of rational numbers (which are, de facto, the default sets used in most professions) is defined as the multiplication of a by the multiplicative inverse of b. Alternative definitions are also based on a multiplication.
That’s why divisions are called an auxilliary operation.
Yes, it is.
I’m defining the division operation, not the quotient. Yes, the quotient is obtained by dividing… Now define dividing.
The actual is the one I gave. I did not give the alternative definitions. That’s why I said they are also defined based on a multiplication, implying the non-alternative one (understand, the actual one) was the one I gave.
Feel free to send your entire Euler document rather than screenshotting the one part you thought makes you right.
Note, by the way, that Euler isn’t the only mathematician who contributed to the modern definitions in algebra and arithmetics.