Math Problem Statement

Describe and correct the error a student made when dividing complex numbers. Given the division \( \frac{1+i}{3-i} \), identify and explain the mistake in the student's solution shown in the image.

Solution

Based on the image provided, the question requires describing and correcting the student's error when dividing complex numbers.

Analysis:

  1. The problem is about dividing 1+i3i\frac{1+i}{3-i}.
  2. The correct method to divide complex numbers involves multiplying both numerator and denominator by the complex conjugate of the denominator, 3+i3+i, not their respective conjugates.

The Student's Error:

The student multiplied both the numerator and denominator by their own complex conjugates instead of multiplying both by the complex conjugate of the denominator. This error is indicated by option B in the provided choices.

Correct Answer:

The correct process should involve:

  1. Multiplying the numerator and denominator by 3+i3+i (the complex conjugate of 3i3-i). 1+i3i3+i3+i=(1+i)(3+i)(3i)(3+i)\frac{1+i}{3-i} \cdot \frac{3+i}{3+i} = \frac{(1+i)(3+i)}{(3-i)(3+i)}
  2. Simplifying the numerator and denominator:
    • Numerator: (1+i)(3+i)=3+i+3i+i2=3+4i1=2+4i(1+i)(3+i) = 3 + i + 3i + i^2 = 3 + 4i - 1 = 2 + 4i
    • Denominator: (3i)(3+i)=32(i2)=9+1=10(3-i)(3+i) = 3^2 - (-i^2) = 9 + 1 = 10 Result: 2+4i10=210+4i10=15+2i5.\text{Result: } \frac{2+4i}{10} = \frac{2}{10} + \frac{4i}{10} = \frac{1}{5} + \frac{2i}{5}.

Final Correct Answer:

15+2i5\frac{1}{5} + \frac{2i}{5}

Would you like further clarification on any of the steps? Here are some related questions:

  1. Why is multiplying by the complex conjugate necessary in division of complex numbers?
  2. What are the rules for simplifying imaginary numbers like i2i^2?
  3. How would the process change if the numerator were not 1+i1+i but something more complex?
  4. How can you check your work when dividing complex numbers?
  5. Are there other applications for the conjugate method in complex arithmetic?

Tip: Always simplify the final result of complex number calculations to standard form a+bia + bi, where aa and bb are real numbers.

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Math Problem Analysis

Mathematical Concepts

Complex Numbers
Complex Conjugates
Division of Complex Numbers
Imaginary Numbers

Formulas

Complex conjugate of (a + bi) is (a - bi)
Multiplication of complex numbers: (a + bi)(c + di) = (ac - bd) + (ad + bc)i
Simplification: i^2 = -1

Theorems

Multiplication by the Conjugate for Division of Complex Numbers

Suitable Grade Level

Grades 10-12