If the operation be performed, we obtain (Art. 66)^

3a — 6^-hc — 2{£.
70. It will be observed that in the former case the signs
of the terms within the parenthesis are unchanged when the
parenthesis is removed ; while in the latter case the sign of
each term within is changed, from + to — , or from — to -f.
Hence, we have the following rule for the removal of a paren-
thesis :

If the parenthesis is preceded by a -\' sign, it may be re-
moved if the sign of every enclosed term be unchanged ; and
if the parenthe&is is preceded by a — sign, it may be removed
if the sign of every enclosed term be changed.
71. To enclose any number of terms in a parenthesis, we
take the reverse of the preceding rule :

Any number of terms may be enclosed in a parenthesis, with
a -h sign prefixed, if the sign of every term enclosed be un*
changed ; and in a parenthesis, with a ^ sign prefixed, if
the sign of every term enclosed be changed.
USE OF PARENTHESES. 23

72. As the bracket, brace, and vinculum (Art. 25) have the
same signification as the parenthesis, the rules for their re-
moval or introduction are the same. It should be observed
in the case of the vinculum, that the sign apparently prefixed
to the first term underneath is in reality the sign of the vin-
culum; thus, -\-a — b signifies 4-(a — />), and — a — 6 signi-
fies — (a — b),

73. ^Parentheses will often be found enclosing others; in
this case they may be removed successively, by the preceding
rule ; and it is better to begin by removing the inside pair.
