Complex Analysis : Complex Numbers

Study concepts, example questions & explanations for Complex Analysis

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Example Questions

Example Question #1 : Complex Numbers

Evaluate: \displaystyle \left| 1 - 3 i \right|

Possible Answers:

\displaystyle \sqrt{10}

\displaystyle - \sqrt{10}

\displaystyle \frac{\sqrt{10}}{2}

\displaystyle 10

Correct answer:

\displaystyle \sqrt{10}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| 1 - 3 i \right| = \sqrt{ 1 + 9 }

\displaystyle = \sqrt{ 10 }

Example Question #2 : Complex Numbers

Evaluate:

\displaystyle \left| 9 - 9 i \right|

Possible Answers:

\displaystyle - 9 \sqrt{2}

\displaystyle 162

\displaystyle 9 \sqrt{2}

\displaystyle \frac{9 \sqrt{2}}{2}

Correct answer:

\displaystyle 9 \sqrt{2}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| 9 - 9 i \right| = \sqrt{ 81 + 81 }

\displaystyle = \sqrt{ 162 }

\displaystyle = 9 \sqrt{2}

Example Question #3 : Complex Numbers

Evaluate:

\displaystyle \left| 6 - 3 i \right|

Possible Answers:

\displaystyle 3 \sqrt{5}

\displaystyle \frac{3 \sqrt{5}}{2}

\displaystyle - 3 \sqrt{5}

\displaystyle 45

Correct answer:

\displaystyle 3 \sqrt{5}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| 6 - 3 i \right| = \sqrt{ 36 + 9 }

\displaystyle = \sqrt{ 45 }

\displaystyle = 3 \sqrt{5}

Example Question #4 : Complex Numbers

Evaluate:

\displaystyle \left| ( 9 + 7 i ) ( -5 + 6 i ) \right|

Possible Answers:

\displaystyle \sqrt{7930}

\displaystyle - \sqrt{7930}

\displaystyle \frac{\sqrt{7930}}{2}

\displaystyle 7930

Correct answer:

\displaystyle \sqrt{7930}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 9 + 7 i ) ( -5 + 6 i ) \right| = \sqrt{ 81 + 49 }\cdot \sqrt{ 25 + 36 }

\displaystyle = \sqrt{130} \cdot \sqrt{61}

\displaystyle = \sqrt{7930}

Example Question #5 : Complex Numbers

Evaluate:

\displaystyle \left| ( 9 + 2 i ) ( -9 + 4 i ) \right|

Possible Answers:

\displaystyle 8245

\displaystyle \frac{\sqrt{8245}}{2}

\displaystyle \sqrt{8245}

\displaystyle - \sqrt{8245}

Correct answer:

\displaystyle \sqrt{8245}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 9 + 2 i ) ( -9 + 4 i ) \right| = \sqrt{ 81 + 4 }\cdot \sqrt{ 81 + 16 }

\displaystyle = \sqrt{85} \cdot \sqrt{97}

\displaystyle = \sqrt{8245}

Example Question #6 : Complex Numbers

Evaluate:

\displaystyle \left| ( 7 + 6 i ) ( -8 + 6 i ) \right|

Possible Answers:

\displaystyle - 10 \sqrt{85}

\displaystyle 8500

\displaystyle 10 \sqrt{85}

\displaystyle 5 \sqrt{85}

Correct answer:

\displaystyle 10 \sqrt{85}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 7 + 6 i ) ( -8 + 6 i ) \right| = \sqrt{ 49 + 36 }\cdot \sqrt{ 64 + 36 }

\displaystyle = \sqrt{85} \cdot 10

\displaystyle = 10 \sqrt{85}

Example Question #7 : Complex Numbers

Evaluate:

\displaystyle \left| ( 5 + 6 i ) ( -8 + 5 i ) \right|

Possible Answers:

\displaystyle 5429

\displaystyle - \sqrt{5429}

\displaystyle \sqrt{5429}

\displaystyle \frac{\sqrt{5429}}{2}

Correct answer:

\displaystyle \sqrt{5429}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 5 + 6 i ) ( -8 + 5 i ) \right| = \sqrt{ 25 + 36 }\cdot \sqrt{ 64 + 25 }

\displaystyle = \sqrt{61} \cdot \sqrt{89}

\displaystyle = \sqrt{5429}

Example Question #8 : Complex Numbers

Evaluate:

\displaystyle \left| ( 10 + 3 i ) ( -5 + 4 i ) \right|

Possible Answers:

\displaystyle 4469

\displaystyle \frac{\sqrt{4469}}{2}

\displaystyle \sqrt{4469}

\displaystyle - \sqrt{4469}

Correct answer:

\displaystyle \sqrt{4469}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 10 + 3 i ) ( -5 + 4 i ) \right| = \sqrt{ 100 + 9 }\cdot \sqrt{ 25 + 16 }

\displaystyle = \sqrt{109} \cdot \sqrt{41}

\displaystyle = \sqrt{4469}

Example Question #9 : Complex Numbers

Evaluate:

\displaystyle \left| ( 9 + i ) ( -9 + 6 i ) \right|

Possible Answers:

\displaystyle 3 \sqrt{1066}

\displaystyle 9594

\displaystyle - 3 \sqrt{1066}

\displaystyle \frac{3 \sqrt{1066}}{2}

Correct answer:

\displaystyle 3 \sqrt{1066}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 9 + i ) ( -9 + 6 i ) \right| = \sqrt{ 81 + 1 }\cdot \sqrt{ 81 + 36 }

\displaystyle = \sqrt{82} \cdot 3 \sqrt{13}

\displaystyle = 3 \sqrt{1066}

Example Question #10 : Complex Numbers

Evaluate:

\displaystyle \left| ( 8 + 5 i ) ( -5 + 5 i ) \right|

Possible Answers:

\displaystyle \frac{5 \sqrt{178}}{2}

\displaystyle 4450

\displaystyle - 5 \sqrt{178}

\displaystyle 5 \sqrt{178}

Correct answer:

\displaystyle 5 \sqrt{178}

Explanation:

The general formula to figure out the modulus is

\displaystyle \left|a+bi\right|=\sqrt{a^2+b^2}

We apply this to get

\displaystyle \left| ( 8 + 5 i ) ( -5 + 5 i ) \right| = \sqrt{ 64 + 25 }\cdot \sqrt{ 25 + 25 }

\displaystyle = \sqrt{89} \cdot 5 \sqrt{2}

\displaystyle =5 \sqrt{178}

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