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MATHEMATICAL EQUATIONS
47-7
If
q3
+
r2
>
0,
one real root and a pair of complex
q3
+
r2
=
0,
all roots real and at least two are
q3
+
r2
<
0,
all roots real (irreducible case)
conjugate roots
equal
Let
s1
=
[r
+
(q3
+
r2)112]113
s2
=
[r
-
(q3
+
r2)112]1’3
then
Solution
of
Quartic Equations*
Given
z4
+
a3Z3
+
a2z2
+
alz
+
a.
=
0,
find the
real root
u1
of the cubic equation
u3
-
a2u2
+
(ala3
-
4ao)U
-
(aI2
+
aoa32
-
4aoa2)
=o
and determine the four roots of the quartic as solutions
of the two quadratic equations
+
(UlI2)
T
[(u1/2)2
-
.oll’z
=
0
If
all roots of the cubic equation are real, use the
value of
uI
that gives real coefficients in the quadratic
equation.
Complex Quantities
In the following equations, all quantities are real
except
j
=
(-I)”~.
(A
+
jB)
+
(C
+
jD)
=
(A
+
C)
+
j(B
+
D)
(A
+
jB)(C
+
jD)
=
(AC
-
BD)
+
j(BC
+
AD)
A+jB AC+BD BC-AD
C+jD C2+D2 ‘jC2+D2
-=
-
*
Abramovitz,
M.
and Stegun,
I.
A.
Handbook
of
Mathe-
mafical
Functions.
Washington,
D.
C.:
National Bureau
of
Standards.
A B
A2
+
B2
-Jm
-- --
I
A
+
jB
Polar Form:
A
+
jB
=
p(cos0
+
j
sine)
=
pd8
De Moivre’s
Equation:
(A
+
jB)”
=
p”(cosv8
+
j
sinve)
where,
p
=
(A2
+
B2)112
>
0,
sine
=
Blp.
case
=
~/p,
For nonintegral v, this quantity is many-valued.
Complex Conjugate:
A
+
jB
=
(A
+
jB)*
=
A
-
jB
Analytic Function:
Let
f(z)
be a function of the
complex variable
z
=
x
+
jy.
Functionf(z) is analytic at
a point z
=
zo,
if
lim
[f(zo
+
Az)
-
f(zo)]/Az
Az-tO
exists independent of the manner in which
Az
ap-
proaches zero. Analyticity is equivalent to the existence
of a Taylor series about the point in question. In
addition,
f(z)
is analytic if and only if the Cauchy-
Riemann equations hold:
auiax
=
aviay
where,
u
=
Ref(z),
v
=
Imf(z).
Iff(z) is analytic for all
z,
it is called an entire function.
Properties
of
e
al
e
=
lim
(1
+
n-’)”
=
2
@!)-I
=
2.71828
e?jx
=
cosx
rfi
j
sinx
=
exp(kjx)
n+m
k=O
Properties
of
Logarithms
If logax
=
N,
then
aN
=
x
logax
=
logab logbx
log,ny
=
logun
+
log,y
log,x/y
=
logax
-
loguy