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\( |4 z-6|=|z+3| \) The solution set is

Ask by Bradley Ayala. in the United States
Feb 25,2025

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Answer

The solution set is all complex numbers \( z \) such that \( |z - \frac{9}{5}| = \frac{6}{5} \).

Solution

We start with the equation   |4z – 6| = |z + 3|. Step 1. Write z in the form x + yi, where x and y are real numbers. Step 2. Express each modulus in terms of x and y:   |4z – 6| = |4(x + yi) – 6| = |(4x – 6) + 4yi| = √[(4x – 6)² + (4y)²],   |z + 3| = |(x + 3) + yi| = √[(x + 3)² + y²]. Step 3. Square both sides to eliminate the square roots:   (4x – 6)² + 16y² = (x + 3)² + y². Step 4. Expand and simplify:   (16x² – 48x + 36) + 16y² = x² + 6x + 9 + y². Subtract the right side from the left:   16x² – 48x + 36 + 16y² – x² – 6x – 9 – y² = 0. Combine like terms:   15x² – 54x + 27 + 15y² = 0. Step 5. Divide the whole equation by 15 to simplify:   x² + y² – (54/15)x + (27/15) = 0,   x² + y² – (18/5)x + (9/5) = 0. Step 6. Complete the square for the x-terms:   x² – (18/5)x = (x – 9/5)² – (9/5)²  since (x – 9/5)² = x² – (18/5)x + (81/25). Substitute back into the equation:   (x – 9/5)² – (81/25) + y² + (9/5) = 0. Step 7. Bring the constants to the right-hand side:   (x – 9/5)² + y² = (81/25) – (9/5). Convert (9/5) to twenty-fifths:   (9/5) = (45/25), Thus,   (x – 9/5)² + y² = (81/25 – 45/25) = 36/25. Step 8. Recognize the equation of a circle:   (x – 9/5)² + y² = (6/5)². Thus, in terms of the complex number z, the solution set is the circle given by   |z – 9/5| = 6/5. So, the solution set is all complex numbers z such that |z – 9/5| = 6/5.

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To solve the equation \( |4z-6| = |z+3| \), we can set up two cases based on the definition of absolute value. The first case occurs when both expressions inside the absolute value are equal, and the second when they are equal in magnitude but opposite in sign. **Case 1:** \( 4z - 6 = z + 3 \) leads to \( 4z - z = 3 + 6 \Rightarrow 3z = 9 \Rightarrow z = 3\). **Case 2:** \( 4z - 6 = -(z + 3) \) leads to \( 4z - 6 = -z - 3 \Rightarrow 4z + z = 6 - 3 \Rightarrow 5z = 3 \Rightarrow z = \frac{3}{5}\). Thus, the solution set is \( \{3, \frac{3}{5}\} \).

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