
Algebra 
23 
. . . 
(Ixl< 
1) 
1  (l+x)-Y* =1--x+-x2--xxJ+-x4 1  2  14  35 
- 
G= 
3 
9 
81  243 
33 1 
3 
~~=(1+X)"=l--x+-x~--xxJ+-x4-. 
2  8  16  128 
. . 
(Ixl< 1) 
with corresponding formulas for (1 
- 
x)'",  etc., obtained by  reversing the signs 
of  the  odd powers  of x. 
Also, 
provided  lbl 
< 
(a(: 
(a+b)" =an(l+$)" 
=a"+nla"-'b+n2a"-2b2+n,a"-'bb"+ 
. 
.. 
where nl, n2, etc., have th  values given  above. 
Progressions 
In an 
arithmetic progression, 
(a, a 
+ 
d, a 
+ 
2d, a 
+ 
3d, 
. . 
.), 
each term is  obtained 
from the preceding term by  adding a constant difference, d. If  n is  the number 
of terms, the last term is p 
= 
a 
+ 
(n 
- 
l)d, the "average" term is  1/2(a 
+ 
p) and 
the sum of  the terms is n times the average term 
or 
s 
= 
n/2(a 
+ 
p). The 
arithmetic 
mean 
between  a and b is  (a 
+ 
b)/2. 
In a 
geometric progression, 
(a, ar, ar2, 
ar', 
. . 
.), 
each term is  obtained from the 
preceding  term  by  multiplying 
by 
a constant ratio,  r.  The nth  term 
is 
a?',  and 
the sum of  the first n  terms is 
s 
= 
a(r" 
- 
l)/(r 
- 
1) 
= 
a(l 
- 
rn)/(l 
- 
r). If 
r 
is  a 
fraction, 
r" 
will approach zero as n increases and the sum of 
n 
terms will approach 
a/( 1 
- 
r) 
as a limit. The 
geometric mean, 
also called the "mean proportional," between 
a and b is 
Jab. 
The 
harmonic  mean 
between a and b is  2ab/(a 
+ 
b). 
Summation of  Series 
by 
Difference Formulas 
a,, a2, 
. . 
., 
an is a series of  n numbers, and 
D' 
(first difference), 
D" 
(second 
difference), 
. . . 
are found by  subtraction  in each column  as follows: 
a 
D' 
D" 
D"'  D"" 
-26 
2 
14 
17 
18 
24 
42 
28 
12 
3 
1 
6 
18 
-16 
-9 
-2 
5 
12 
0 
0 
0