Complex Nos

1 ) if iiiiii...∞ = a+ib

prove that tan 1/2 pi a = b/a and a2+b2=e-pib...

2) if z1 and z1 are the roots of the equation αz2+βz+γ=0
prove that |z1|+|z2| = 1/|α|[ |-β+√αγ|+|-β-√αγ|]

8 Answers

11
Tush Watts ·

Ans 1) i i i i .....∞ = a + i b
i a+ i b = a + i b

Now, a + i b = i a+ i b = e(a+i b ) log i [Taking Principal values only]

= e(a+i b ) log (cos pie/2 + i sin pie/2)i
= e(a+i b ) log (e i pie/2)
= e(a+i b ) i pie/2 = e - ( b pie/2) + i (a pie/2)
= e - b pie/2 . e i a pie/2

= e - b pie/2 (cos a pie/2 + i a sin pie/2)
Equating real and imaginary parts, we get

a = e - b pie/2 cos (a pie/2) .........................(i)
b = e - b (pie/2) sin (a pie/2) .........................(ii)

Dividing (ii) by (i) ,
tan (a pie/2) = b/a

Squaring and adding (i) and (ii), we get
a2 + b2 = e - b pie [cos 2( apie/2) + sin 2 (a pie/2)] = e - b pie

Thus Proved

11
Aditya Balasubramanyam ·

thanx tushar

11
Aditya Balasubramanyam ·

one more dbt

if |z1|=|z2|=|z3| and z1 z2 z3 are the vertices of an equilateral triangle such that z1+z2+z3=0 prove that this triangle is inscribed in a circle of unit radius

1
Che ·

i guess u cant prove it to be inscribe in a circle of unit radius unless |z1|=|z2|=|z3| =1

centriod here is origin z1+z2+z3/3=0/3=0
for equil trian circumcenter is also centriod

so circumcent is origin and if it wud hav been given |z1|=|z2|=|z3|=1 then we wud hav proved that tat circle is of unit radius

11
Aditya Balasubramanyam ·

that is what u have 2 prove ... |z|=1 [22]

1
Che ·

nope check the q again

11
Aditya Balasubramanyam ·

ya checked ...... it s from arihant

11
Aditya Balasubramanyam ·

ya checked ...... it s from arihant and i 've solved it also...

somebody pls try q2

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