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