[PDF] 1 Basics of Series and Complex Numbers



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Instruction: This Part II of Form 1-Z is required by Rule 257(d) of Regulation A An officer of the issuer or any other duly authorized person may sign, and must do so by typed signature The name and title of the person signing the form must be typed or printed under the signature The signatory to the filing must also manually



1 Basics of Series and Complex Numbers

1 1 z = 1 + z+ z2 + = X1 n=0 zn (19) is the Taylor series of f(z) = 1=(1 z) about z= 0 As mentioned earlier, the function 1=(1 z) exists and is in nitely di erentiable everywhere except at z= 1 while the series P 1 n=0 z nonly exists in the unit circle jzj



Lecture 22: Inverse Functions - Furman

1+z 1−z Hence w = 1 2 log 1+z 1−z Thus we define the inverse hyperbolic tangent function by tanh−1(z) = 1 2 log 1+z 1−z We find the other inverse hyperbolic trigonometric functions in a similar manner The most important of these are sinh−1(z) = log z +(z2 +1)12 and cosh−1(z) = log z +(z2 −1)12 The derivatives are d dz sinh



Topic 8 Notes Jeremy Orlo - MIT Mathematics

f(z) = z+ 1 z3(z2 + 1) has isolated singularities at z= 0; iand a zero at z= 1 We will show that z= 0 is a pole of order 3, z= iare poles of order 1 and z= 1 is a zero of order 1 The style of argument is the same in each case At z= 0: f(z) = 1 z3 z+ 1 z2 + 1: Call the second factor g(z) Since g(z) is analytic at z= 0 and g(0) = 1, it has a



Functions of a Complex Variable - MIT OpenCourseWare

1 z + 1 dz 2 −1 z is −2 − i if the path is the upper half of the circle r = 1 [Write z = ei , where varies from to 0, or from (2k + 1) to 2k , where k is any integer ] (b) Show (also by direct integration) that the value is −2 + i if the path is the lower half of the circle



72 Complex arithmetic - mathcentreacuk

j2 = −1 If z 1 and z2 are the two complex numbers their product is written z1z2 Example If z1 = 5− 2j and z2 = 2+4j find z1z2 Solution z1z2 = (5− 2j)(2+4j) = 10+20j −4j − 8j2 Replacing j2 by −1 we obtain z1z2 = 10+16j −8(−1) = 18+16j In general we have the following result: www mathcentre ac uk 7 2 1 c Pearson Education Ltd 2000



SOLUTIONS TO HOMEWORK ASSIGNMENT &# 7

z2 +z +1 z=e2πı/3 = 2πı 1 2z +1 z=e2πı/3 = 2π √ 3 (b) The only singularity of z2e1/z sin(1/z) occurs at z = 0, and it is an essential singularity Therefore the formula for computing the residue at a pole will not work, but we can still compute some of the coefficients in the Laurent series expansion about z = 0 : z2e1/z sin(1/z) = z2



7 Taylor and Laurent series - MIT Mathematics

1 w z which looks a lot like the sum of a geometric series We will make frequent use of the following manipulations of this expression 1 w z = 1 w 1 1 z=w = 1 w 1 + (z=w) + (z=w)2 + ::: (3) The geometric series in this equation has ratio z=w Therefore, the series converges, i e the formula is valid, whenever jz=wj

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1 Basics of Series and Complex Numbers

ComplexNumbersandExponentials

numbers(x1;y1)and(x2;y2)isdenedby (x1;y1)+(x2;y2)=(x1+x2;y1+y2) (x1;y1)(x2;y2)=(x1x2y1y2;x1y2+x2y1) by z

1+z2=(x1+x2)+i(y1+y2)

z

1z2=x1x2y1y2+i(x1y2+x2y1)

Thecomplexnumberihasthespecialproperty

i

2=(0+1i)(0+1i)=(0011)+i(01+10)=1

Forexample,ifz=1+2iandw=3+4i,then

z+w=(1+2i)+(3+4i)=4+6i z

1+z2=z2+z1z1z2=z2z1

z

1+(z2+z3)=(z1+z2)+z3z1(z2z3)=(z1z2)z3

0+z1=z11z1=z1

z

1(z2+z3)=z1z2+z1z3(z1+z2)z3=z1z3+z2z3

z=xx2+y2yx2+y2iandobeys1zz=1.

Toverifythat1

zz=1,justmultiplyout x

Thedenition1

realnumber.Forexample 11+2i

25=1125+225i

example,supposethatwewanttond1+2i 1+2i conjugate,onereplaceseveryibyi.Notethat zz=(x+iy)(xiy)=x2ixy+ixy+y2=x2+y2 1 jzj=p x2+y2=pzz

Sincejzj2=zz,wehave

z 1=z jzj2 jz1z2j=p (x1x2y1y2)2+(x1y2+x2y1)2 q =q =jz1jjz2j forallcomplexnumbersz1;z2.

Rez=xImz=y

Rez=1

2(z+z)Imz=12i(zz)

TheComplexExponential

e x+iy=excosy+iexsiny n=0xn n!. e iy=1+iy+(iy)2

2!+(iy)33!+(iy)44!+(iy)55!+(iy)66!+

Theeventermsinthisexpansionare

1+(iy)2

2!+(iy)44!+(iy)66!+=1y22!+y44!y66!+=cosy

andtheoddtermsinthisexpansionare iy+(iy)3

3!+(iy)55!+=i

yy33!+y55!+ =isiny 2

Foranytwocomplexnumbersz1andz2

e z1ez2=ex1(cosy1+isiny1)ex2(cosy2+isiny2) =ex1+x2(cosy1+isiny1)(cosy2+isiny2) =ex1+x2fcos(y1+y2)+isin(y1+y2)g =e(x1+x2)+i(y1+y2) =ez1+z2 a=+iandrealnumbert e at=et+it=et[cos(t)+isin(t)] sothatthederivativewithrespecttot d =(+i)et[cos(t)+isin(t)] =aeat isalsothefamiliarone. e i=cos+isin e i=cosisin= ei cos=1

2(ei+ei)=Reei

sin=1

2i(eiei)=Imei

coscos=1

4(ei+ei)(ei+ei)

1

4(ei(+)+ei()+ei(+)+ei(+))

1

4(ei(+)+ei(+)+ei()+ei(+))

1

2cos(+)+cos()

and,using(a+b)3=a3+3a2b+3ab2+b3, sin 3=1

8ieiei3

=1

8iei33ei+3eiei3

3

412ieiei1412iei3ei3

3

4sin14sin(3)

waygives x+iy=rcos+irsin=rei y xx+iy=rei r 3

Inparticular

y x 2 2

1=(1;0)(1;0)=1i=(0;1)

i=(0;1)1=ei0=e2i=e2kifork=0;1;2;

1=ei=e3i=e(1+2k)ifork=0;1;2;

i=ei=2=e5

2i=e(12+2k)ifork=0;1;2;

i=ei=2=e3

2i=e(12+2k)ifork=0;1;2;

z n=1

Writingz=rei

r neni=1e0i ofunitybecausee2ik

1;e2i1

n;e2i2n;e2i3n;;e2in1n y x

1=e2i0

6e 2i1

6e2i26

e 2i3 6=1 e 2i4

6e2i56

Example1Z

e xcosxdx=1 2Z e xeix+eixdx=12Z e(1+i)x+e(1i)xdx 1 2

11+ie(1+i)x+11ie(1i)x+C

real,despitethei's,because1

1+i=1i(1+i)(1i)=1i2and

1 1i= 1

1+i=1+i2.Z

e xcosxdx=1

2ex11+ieix+11ieix+C

1

2ex1i2(cosx+isinx)+1+i2(cosxisinx)+C

1

2excosx+12exsinx+C

4 Z cos

4xdx=1

1

2414ie4ix+42ie2ix+6x+42ie2ix+14ie4ix+C

1

241212i(e4ixe4ix)+42i(e2ixe2ix)+6x+C

1

2412sin4x+4sin2x+6x+C

1

32sin4x+14sin2x+38x+C

y

00+2y0+3y=cost(1)

Y

00+2Y0+3Y=eit(2)

Then,takingcomplexconjugates,

Y00+2Y0+3Y=eit(2)

and,adding1

2(2)and12(2)togetherwillgive

(ReY)00+2(ReY)0+3(ReY)=Reeit=cost d 2 dt2Aeit+2ddtAeit+3Aeit=eit ()(2+2i)Aeit=eit ()A=1 2+2i

Sowehavefoundasolutionto(2)andReeit

coordinates.So

2+2i=2p

2ei4)eit2+2i=eit2p2ei4=12p2ei(t

4))Reeit2+2i=12p2cos(t4)

Example4Inthisexample,weshallndRp

x21dx.

1x2dx,we

1x2=p1cos2t=psin2t.Nowthat

x21=pcos2t1=psin2t=p1psin2t=isint. x21dxwillonlyincludex'sobeyingx21, sothatp 5 d throughtherealnumbersfrom0toinnity,1 function 1 zissinhz=1 cosy=coshiyisiny=sinhiy sin 2ezez andcoshz=1 cos,uptosigns.Forexample,whiled dxcosx=sinx,ddxcoshx=sinhx.

2ez+ez

x=1

2ez+ez

dx=1

2ezezdz

x 21=1

4ez+ez21=14e2z+2+e2z1=14e2z2+e2z=14ezez2

p x21=12ezez p x21dx=14ezez2dz=14e2z2+e2zdzZp x21dx=14Z e2z2+e2zdz=14

12e2z2z12e2z+C

2ez+ezforzasa

functionofx. x=1 hastwosolutions:Q=1

Q.Oneofthetwosolutionsxp

havetochooseez=x+p x21andez=xpx21.Asacheck,notethat x+p x21xpx21=x2(x21)=1)1x+px21=xpx21

Subbinginez=x+p

x21andez=xpx21andz=lnx+px21,Zp x21dx=14

12e2z2z12e2z+C

1 4

12x+px2122lnx+px2112xpx212+C

1

2xpx21lnx+px21+C

Asacheck,notethat

d dx12xpx21lnx+px21=12h px21+xxpx211+x=p x21 x+px21i 1 2h x21px21+x2px211px21p x21+x x+px21i 1 2h x21px21+x2px211px21i 1 2h

2x22px21i

x21px21=px21 asdesired. 6 ofaquadraticequation:2p 2245
2=2p 420

2=1p4=12i.Orwecancompletethesquare

x

Nextwewritetheintegrandintheform

x+2 withtheconstantsaandbchosensothat a wechoosex+1=2i:

4i=1214i

4i=12+14i

since 1 a(x+1+2i)+b(x+12i)=1

214i(x+1+2i)+12+14i(x+12i)

=(x+1)1

214i+12+14i+2i1214i1214i

=x+1+2i1

2i=x+2

asdesired.Theintegralisnoweasy, Z x+2 x2+2x+5dx=Z h ax+12i+bx+1+2ii dx=aln(x+12i)+bln(x+1+2i)+C 1

214iln(x+12i)+12+14iln(x+1+2i)+C

ln(XiY)=lnp

X2+Y2itan1YX(L)

e equationsgivestanV=Y

Applying(L)withX=x+1andY=2gives

1 1

2+14ipx2+2x+5+itan12x+1

p x2+2x+512tan12x+1 7quotesdbs_dbs31.pdfusesText_37