What does $\cos(\pi-\overline{B+C})$ mean?

Question

Here $A$, $B$ and $C$ are three angles of a triangle, so $A+B+C=\pi$. Now, my book did the following:

$$\cos A$$

$$=\cos(\pi-\overline{B+C})\tag{1}$$

$$=-\cos(B+C)$$

My comments:

In $\cos(\pi-\overline{B+C})$, there seems to be no special meaning to the overline to me. $\cos(\pi-\overline{B+C})$ and $\cos(\pi-(B+C))$ seem to be equal. In other words, to me the following seems to be true:

$$\cos(\pi-\overline{B+C})=\cos(\pi-(B+C))$$

So, why did my book put the overline symbol over $B+C$? What meaning does it hold?

My question:

1. What meaning does the overline symbol hold in $(1)$?

Answer 1

For an example of the bar being used as a pair or parentheses, see for example p.397 of Cajori, F. A History of Mathematical Notations, Dover 1993 which seems to be a reprint of the 1928 edition. If pages are changed, look for article 353. Contrary to what I wrote, it is rather used in the 17th and 18th centuries although it could have existed longer than that.