Question Details

Let z be a complex number satisfying z3+2z2+4z¯8=0, where z¯ denotes the complex conjugate of z. Let the imaginary part of z be nonzero. Match each entry in List-I to the correct entries in List-II.


List-I List-II
(P) | z | 2 is equal to (1) 12
(Q) | z z ¯ | 2 is equal to (2) 4
(R) | z | 2 + | z + z ¯ | 2 is equal to (3) 8
(S) | z + 1 | 2 is equal to (4) 10
(5) 7



Options

A

(P) → (1), (Q) → (3), (R) → (5), (S) → (4)

B

(P) → (2), (Q) → (1), (R) → (3), (S) → (5)

C

(P) → (2), (Q) → (4), (R) → (5), (S) → (1)

D

(P) → (2), (Q) → (3), (R) → (5), (S) → (4)

Show Answer

Correct Answer :

Option B

(P) → (2), (Q) → (1), (R) → (3), (S) → (5)

Solution :

The correct option is (P) → (2), (Q) → (1), (R) → (3), (S) → (5).

Step 1: Finding the real part of z

We are given the complex equation:

z3+2z2+4z¯8=0

Taking the complex conjugate of the entire equation, since z3 and 8 are real numbers, we get:

z3+2z¯2+4z8=0

Subtracting the original equation from its conjugate equation gives:

2z¯2z2+4zz¯=0

Factoring out z¯z:

2z¯zz¯+z4z¯z=0

2z¯zz+z¯2=0

Since the imaginary part of z is non-zero, zz¯, which means z¯z0. Therefore:

z+z¯2=0z+z¯=2

Since z+z¯=2Rez, we have Rez=1.

Step 2: Finding the modulus z and imaginary part

Let z=1+iy with y0. Then:

z2=1+iy2=1y2+2iy

z¯=1iy

Substitute z, z2, and z¯ into the original equation:

z3+21y2+2iy+41iy8=0

Simplifying the terms:

z3+22y2+4iy+44iy8=0

z32y22=0

Since z2=1+y2, we have y2=z21. Substituting this gives:

z32z212=0

z32z2=0

z2z2=0

Since z>0, we obtain:

z=2

Therefore:

z2=4

Also, y2=z21=41=3.

Step 3: Evaluation of List-I entries

(P) z2:

z2=4

Thus, (P) → (2).

(Q) zz¯2:

zz¯=1+iy1iy=2iy

zz¯2=2iy2=4y2=4×3=12

Thus, (Q) → (1).

(R) z2+z+z¯2:

z+z¯=2z+z¯2=22=4

z2+z+z¯2=4+4=8

Thus, (R) → (3).

(S) z+12:

z+1=1+iy+1=2+iy

z+12=22+y2=4+3=7

Thus, (S) → (5).

Combining all the matches:

(P) → (2), (Q) → (1), (R) → (3), (S) → (5)

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