-4 -3 -2 -1 +1 +2 +3 +4

I I I I I I I I i

Thus,- the result of subtracting -f- 1 from + 3 is found
by coimting from + 3 one unit in the negative direction ;
that is, in the direction opposite to that indicated by the sign
+ before 1, and is, therefore, -f- 2.
The result of subtracting — 1 from + 3 is f oimd by
coimting from + 3 one unit in the positive direction, and
is, therefore, + 4.
The result of subtracting + 1 from — 3 is found by
counting from — 3 one imit in the negative direction, and
is, therefore, — 4.
The result of subtracting — 1 from — 3 is found by
coimting from — 3 one unit in the positive direction, and
is, therefore, — 2.
If a and b represent any two numbers, we have
+ a - (+ J) = a - ^. -a-(+b) = '-a-b.
+ a - (- 5) = a + ^. - a - (- J) = - a + ^.
74. From these four cases we see that subtracting a posi-
tive number is equivalent to adding an equal negative num-
ber ; and that subtracting a negative number is equivalent
to adding an egual positive number. Therefore,

75. To Subtract One Algebraic Number from Another,
Change the sign of the subtrahend, and add the result to

the minuend.
Digitized by CjOOQ IC



POSITIVE AND NEGATIVE NUMBERS. 41

EXEBCISB 12.
Perform mentally the indicated subtractions :



1.
2.
3.
4.
6.
6.
11


-11


-11


11


3


- 3


J


- 3


3


- 3


11


-11


7.
8.
9.
10.
11.
12.
