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← JEE Main 2022 · 25 Jun · Shift 2
MathematicsSingle correct+4 / -1Question 3 of 90

JEE Main 2022 · 25 Jun · Shift 2, Mathematics question 3

Let z1z_1 and z2z_2 be two complex numbers such that zˉ1=izˉ2\bar z_1=i\bar z_2 and arg⁡(z1zˉ2)=π\arg\left(\dfrac{z_1}{\bar z_2}\right)=\pi. Then

Choose one option
Answer and worked solution

Official answer: C

Relation. zˉ1=izˉ2\bar z_1=i\bar z_2 gives z1=−iz2z_1=-iz_2, so z1zˉ2=−i e2iθ2\dfrac{z_1}{\bar z_2}=-i\,e^{2i\theta_2} with θ2=arg⁡z2\theta_2=\arg z_2.

Condition. −π2+2θ2≡π-\frac\pi2+2\theta_2\equiv\pi, so θ2=3π4\theta_2=\frac{3\pi}4 or −π4-\frac\pi4, and arg⁡z1=θ2−π2=π4\arg z_1=\theta_2-\frac\pi2=\frac\pi4 or −3π4-\frac{3\pi}4.

Options. A and B are never true. With arg⁡z2=3π4\arg z_2=\frac{3\pi}4, arg⁡z1=π4\arg z_1=\frac\pi4, the keyed (C). Note: arg⁡z2=−π4\arg z_2=-\frac\pi4, arg⁡z1=−3π4\arg z_1=-\frac{3\pi}4 also satisfies both conditions, so (D) is possible too; NTA's key gives (C) only.

(C)