🛠️ JEE➗ Maths

If \(z=\frac{1}{2}-2 i\) is such that \(|z+1|=\alpha z+\beta(1+i), i=\sqrt{-1}\) and \(\alpha, \beta \in \mathbb{R}\), t…

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If \(z=\frac{1}{2}-2 i\) is such that \(|z+1|=\alpha z+\beta(1+i), i=\sqrt{-1}\) and \(\alpha, \beta \in \mathbb{R}\), then \(\alpha+\beta\) is equal to

[JEE Main 2024, 29 Jan (Shift 1)]

a

2

b

-1

c

-4

d

3

✓ Correct answer: d)

3

Explanation

Given

\(z=\frac{1}{2}-2 i\)

\(|z+1|=\alpha z+\beta(1+i)\)

\(\left|\frac{3}{2}-2 i\right|=\frac{\alpha}{2}-2 \alpha i+\beta+\beta i\)

\(\left|\frac{3}{2}-2 i\right|=\left(\frac{\alpha}{2}+\beta\right)+(\beta-2 \alpha) i\)

On comparing

\(\beta=2 \alpha\) and \(\frac{\alpha}{2}+\beta=\sqrt{\frac{9}{4}+4}\)

\(\alpha+\beta=3\)

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