Complex Analysis : Complex Analysis

Study concepts, example questions & explanations for Complex Analysis

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Example Questions

Example Question #1 : Complex Analysis

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

Possible Answers:

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

\(\displaystyle 10\)

\(\displaystyle \sqrt{10}\)

\(\displaystyle - \sqrt{10}\)

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 Analysis

Evaluate:

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

Possible Answers:

\(\displaystyle - 9 \sqrt{2}\)

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

\(\displaystyle 9 \sqrt{2}\)

\(\displaystyle 162\)

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 Analysis

Evaluate:

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

Possible Answers:

\(\displaystyle 45\)

\(\displaystyle 3 \sqrt{5}\)

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

\(\displaystyle - 3 \sqrt{5}\)

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 #1 : Complex Numbers

Evaluate:

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

Possible Answers:

\(\displaystyle 7930\)

\(\displaystyle \sqrt{7930}\)

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

\(\displaystyle - \sqrt{7930}\)

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 Analysis

Evaluate:

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

Possible Answers:

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

\(\displaystyle \sqrt{8245}\)

\(\displaystyle - \sqrt{8245}\)

\(\displaystyle 8245\)

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 Analysis

Evaluate:

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

Possible Answers:

\(\displaystyle 8500\)

\(\displaystyle - 10 \sqrt{85}\)

\(\displaystyle 5 \sqrt{85}\)

\(\displaystyle 10 \sqrt{85}\)

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 #2 : Complex Numbers

Evaluate:

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

Possible Answers:

\(\displaystyle - \sqrt{5429}\)

\(\displaystyle \sqrt{5429}\)

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

\(\displaystyle 5429\)

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 Analysis

Evaluate:

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

Possible Answers:

\(\displaystyle - \sqrt{4469}\)

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

\(\displaystyle \sqrt{4469}\)

\(\displaystyle 4469\)

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 #3 : Complex Numbers

Evaluate:

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

Possible Answers:

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

\(\displaystyle 3 \sqrt{1066}\)

\(\displaystyle - 3 \sqrt{1066}\)

\(\displaystyle 9594\)

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 Analysis

Evaluate:

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

Possible Answers:

\(\displaystyle 5 \sqrt{178}\)

\(\displaystyle 4450\)

\(\displaystyle - 5 \sqrt{178}\)

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

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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