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41 Déterminer et représenter les ensembles de points M du plan dont l'affixe z vérifie la condition indiquée. a) |z+z̄-1|=4 b) |z-z̄-1+i|=2 c) arg(3i-z)≡0 [2π] d) arg(z-3+i)≡π/4 [π] e) arg(1/(z+2))≡π/2 [π] f) arg(z²-4)≡a

Concept: Geometric loci complex numbers

Question

41 Déterminer et représenter les ensembles de points M du plan dont l'affixe z vérifie la condition indiquée.
a) |z+z̄-1|=4
b) |z-z̄-1+i|=2
c) arg(3i-z)≡0 [2π]
d) arg(z-3+i)≡π/4 [π]
e) arg(1/(z+2))≡π/2 [π]
f) arg(z²-4)≡arg(z+2) [2π].

Try it yourself first

Hint: What happens when you substitute z=x+iyz = x + iy into the expression ∣z+zˉ−1∣|z+z̄-1|?

Step-by-step solution

  1. 1

    Problem Statement

    We need to find the set of points M for each given condition.
  2. 2

    Complex Number Basics

    Let z=x+iyz = x + iy, where xx is the real part and yy is the imaginary part.
    z=x+iyz = x + iy
  3. 3

    Substitute and Simplify

    Substitute z=x+iyz = x + iy and zˉ=x−iy\bar{z} = x - iy into the equation and simplify.
  4. 4

    Substitution

    Substitute zz and zˉ\bar{z} into the equation.
    ∣(x+iy)+(x−iy)−1∣=4|(x+iy) + (x-iy) - 1| = 4
  5. 5

    Simplify Expression

    Combine real and imaginary parts.
    ∣2x−1∣=4|2x - 1| = 4
  6. 6

    Solve for x

    The absolute value equation ∣A∣=B|A|=B means A=BA=B or A=−BA=-B.
    2x−1=4or2x−1=−42x - 1 = 4 \quad \text{or} \quad 2x - 1 = -4
  7. 7

    Calculate x values

    Solve the two linear equations for xx.
    2x=5  ⟹  x=5/2or2x=−3  ⟹  x=−3/22x = 5 \implies x = 5/2 \quad \text{or} \quad 2x = -3 \implies x = -3/2
  8. 8

    Geometric Interpretation

    The set of points M are two vertical lines: x=5/2x = 5/2 and x=−3/2x = -3/2.

Final answer

The question asks for multiple parts. I will solve part (a) as an example. The answer for part (a) is the set of points M such that x=5/2x = 5/2 or x=−3/2x = -3/2. This represents two vertical lines.

Remember: Substitute $z=x+iy$ to convert complex equations into Cartesian coordinates.

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Quick check · test yourself

If ∣z−zˉ+3∣=5|z - z̄ + 3| = 5, what is the geometric interpretation of the set of points M?

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