Let z and ω be two complex numbers such that ω = zz? - 2z + 2, |(z + i)/(z - 3i)| = 1 and Re(ω) has minimum value. Then, the minimum value of n ∈ N for which ω? is real, is equal to
Let z and ω be two complex numbers such that ω = zz? - 2z + 2, |(z + i)/(z - 3i)| = 1 and Re(ω) has minimum value. Then, the minimum value of n ∈ N for which ω? is real, is equal to
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1 Answer
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|z+i|/|z-3i| = 1 ⇒ |z+i| = |z-3i|. This means z is on the perpendicular bisector of the segment from -i to 3i. The midpoint is i, so z = x+i.
w = z? - 2z + 2. Let z = x + iy.
w = (x² + y²) - 2 (x + iy) + 2 = (x² - 2x + 2 + y²) - 2iy.
Re (w) = x² - 2x + 2 + y² = (x - 1)² + 1 + y².
From the first condition, y=1. Re (w) = (x - 1)² + 1 + 1 = (x - 1)² + 2.
Re (w) is minimum for x = 1.
The common z is z = 1 + i.
w = (1+i) (1-i) - 2 (1+i) + 2 = 2 - 2 - 2i + 2 = 2 - 2i.
w² = (2 - 2i)² = 4 (1 - 2i - 1) = -8i.
w? = (-8i)² = -64 ∈ R.
∴ least n ∈ N for which w? ∈ R i...more
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