Step-3

Title: Division of complex numbers

Grade: 8-b Lesson: S2-L7

Explanation: Hello Students, time to practice and review the steps for the problem.

Lesson Steps

Discussion: Step1 Step2 Step3 Step4 Step5

Step Type Explanation Answer

1

Problem

Divide \$(5 + 7i)/(3 - 4i)\$ and simplify the result.

2

Step

Given that

\$(5 + 7i)/(3 - 4i)\$

3

Step

Identify the complex conjugate of the denominator:

The complex conjugate of (3 - 4i) is (3 + 4i)

4

Step

Multiply both the numerator and denominator by the complex conjugate:

\$((5 + 7i)(3 + 4i)) / ((3 - 4i)(3 + 4i))\$

5

Step

Expand the numerator:

\$ (5 \times 3) + (5 \times 4i) + (7i \times 3) + (7i \times 4i) \$

\$15 + 20i + 21i + 28i^2\$

15 + 41i - 28 (since \$i^2 = -1\$)

-13 + 41i

6

Step

Expand the denominator:

\$(3 \times 3) + (3 \times 4i) + (-4i \times 3) + (-4i \times 4i)\$

\$9 + 12i - 12i - 16i^2\$

9 + 16 (since \$i^2 = -1\$)

25

7

Step

Simplify the fraction:

\$(-13 + 41i) / 25\$

8

Step

Separate into real and imaginary parts:

\$-13/25 + (41/25)i\$

⇒ -0.52 + 1.64i

9

Step

Therefore, the simplified result of dividing (5 + 7i) by (3 - 4i) is -0.52 + 1.64i.

10

Choice.A

This option is incorrect. While the imaginary part matches our result, the real part should be negative, not positive

1 + 1.64i

11

Choice.B

This option is correct. It matches our calculated result of \$(5 + 7i)/(3 - 4i)\$ which is -0.52 + 1.64i

-0.52 + 1.64i

12

Choice.C

This option is incorrect. The real part should be negative and the imaginary part should be 1.64i, not 1.04i

1 + 1.04i

13

Choice.D

This option is incorrect. The real part is positive when it should be negative, and the imaginary part has the wrong sign

0.52 - 1.64i

14

Answer

Option

B

15

Sumup

Can you summarize what you’ve understood in the above steps?

Discussion: Step1 Step2 Step3 Step4 Step5


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