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| 197 | +<h2 class="unnumbered" id="complex-analysis-may-1977">Complex Analysis, |
| 198 | +May 1977</h2> |
| 199 | +<ol> |
| 200 | +<li><p>Classify the singularities of the following functions, including |
| 201 | +<math role="math" aria-label="z=\infty" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mo>=</mo><mi>∞</mi></mrow><annotation encoding="application/x-tex">z=\infty</annotation></semantics></math>. |
| 202 | +Give orders of poles.<br /> |
| 203 | +(a) |
| 204 | +<math role="math" aria-label="\frac{z}{\sin z}" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mfrac><mi>z</mi><mrow><mrow><mi mathvariant="normal">sin</mi><mo>⁡</mo></mrow><mi>z</mi></mrow></mfrac><annotation encoding="application/x-tex">\frac{z}{\sin z}</annotation></semantics></math><br /> |
| 205 | +(b) |
| 206 | +<math role="math" aria-label="\frac{1}{\left(1+z^{2}\right)(2-z)^{2}}" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mfrac><mn>1</mn><mrow><mrow><mo stretchy="true" form="prefix">(</mo><mn>1</mn><mo>+</mo><msup><mi>z</mi><mn>2</mn></msup><mo stretchy="true" form="postfix">)</mo></mrow><mo stretchy="false" form="prefix">(</mo><mn>2</mn><mo>−</mo><mi>z</mi><msup><mo stretchy="false" form="postfix">)</mo><mn>2</mn></msup></mrow></mfrac><annotation encoding="application/x-tex">\frac{1}{\left(1+z^{2}\right)(2-z)^{2}}</annotation></semantics></math></p></li> |
| 207 | +<li><p>Consider</p></li> |
| 208 | +</ol> |
| 209 | +<p><math role="math" aria-label="f(z)=\frac{1}{\left(1+z^{2}\right)(2-z)^{2}}" display="block" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mo stretchy="false" form="prefix">(</mo><mi>z</mi><mo stretchy="false" form="postfix">)</mo><mo>=</mo><mfrac><mn>1</mn><mrow><mrow><mo stretchy="true" form="prefix">(</mo><mn>1</mn><mo>+</mo><msup><mi>z</mi><mn>2</mn></msup><mo stretchy="true" form="postfix">)</mo></mrow><mo stretchy="false" form="prefix">(</mo><mn>2</mn><mo>−</mo><mi>z</mi><msup><mo stretchy="false" form="postfix">)</mo><mn>2</mn></msup></mrow></mfrac></mrow><annotation encoding="application/x-tex">f(z)=\frac{1}{\left(1+z^{2}\right)(2-z)^{2}}</annotation></semantics></math></p> |
| 210 | +<p>(a) Find its principal part at |
| 211 | +<math role="math" aria-label="z=2" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mo>=</mo><mn>2</mn></mrow><annotation encoding="application/x-tex">z=2</annotation></semantics></math>.<br /> |
| 212 | +(b) In what region does its Laurant series about |
| 213 | +<math role="math" aria-label="z=2" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mo>=</mo><mn>2</mn></mrow><annotation encoding="application/x-tex">z=2</annotation></semantics></math> |
| 214 | +converge?<br /> |
| 215 | +(c) In what circular regions center at |
| 216 | +<math role="math" aria-label="z=0" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>z</mi><mo>=</mo><mn>0</mn></mrow><annotation encoding="application/x-tex">z=0</annotation></semantics></math> |
| 217 | +does |
| 218 | +<math role="math" aria-label="f(z)" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mo stretchy="false" form="prefix">(</mo><mi>z</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">f(z)</annotation></semantics></math> |
| 219 | +have a Laurant expansion?<br /> |
| 220 | +(d) Expand |
| 221 | +<math role="math" aria-label="f(z)" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mo stretchy="false" form="prefix">(</mo><mi>z</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">f(z)</annotation></semantics></math> |
| 222 | +in |
| 223 | +<math role="math" aria-label="1<|z|<2" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mn>1</mn><mo><</mo><mo stretchy="false" form="prefix">|</mo><mi>z</mi><mo stretchy="false" form="prefix">|</mo><mo><</mo><mn>2</mn></mrow><annotation encoding="application/x-tex">1<|z|<2</annotation></semantics></math>.<br /> |
| 224 | +3. Integrate, by complex methods,<br /> |
| 225 | +(a) |
| 226 | +<math role="math" aria-label="\int_{-\pi}^{\pi} \frac{1}{1-a \cos \theta} d \theta, \quad 0<a<1" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msubsup><mo>∫</mo><mrow><mi>−</mi><mi>π</mi></mrow><mi>π</mi></msubsup><mfrac><mn>1</mn><mrow><mn>1</mn><mo>−</mo><mi>a</mi><mrow><mi mathvariant="normal">cos</mi><mo>⁡</mo></mrow><mi>θ</mi></mrow></mfrac><mi>d</mi><mi>θ</mi><mo>,</mo><mspace width="1.0em"></mspace><mn>0</mn><mo><</mo><mi>a</mi><mo><</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">\int_{-\pi}^{\pi} \frac{1}{1-a \cos \theta} d \theta, \quad 0<a<1</annotation></semantics></math>;<br /> |
| 227 | +(b) |
| 228 | +<math role="math" aria-label="\int_{0}^{\infty} \frac{d x}{x^{\alpha}(x+1)^{2}}, \quad 0<\alpha<1" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msubsup><mo>∫</mo><mn>0</mn><mi>∞</mi></msubsup><mfrac><mrow><mi>d</mi><mi>x</mi></mrow><mrow><msup><mi>x</mi><mi>α</mi></msup><mo stretchy="false" form="prefix">(</mo><mi>x</mi><mo>+</mo><mn>1</mn><msup><mo stretchy="false" form="postfix">)</mo><mn>2</mn></msup></mrow></mfrac><mo>,</mo><mspace width="1.0em"></mspace><mn>0</mn><mo><</mo><mi>α</mi><mo><</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">\int_{0}^{\infty} \frac{d x}{x^{\alpha}(x+1)^{2}}, \quad 0<\alpha<1</annotation></semantics></math>.<br /> |
| 229 | +4. Find, if possible, a conformal map of |
| 230 | +<math role="math" aria-label="A" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>A</mi><annotation encoding="application/x-tex">A</annotation></semantics></math> |
| 231 | +onto the upper half plane |
| 232 | +<math role="math" aria-label="\{z: \operatorname{Im} z>0\}" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false" form="prefix">{</mo><mi>z</mi><mo>:</mo><mrow><mi mathvariant="normal">Im</mi><mo>⁡</mo></mrow><mi>z</mi><mo>></mo><mn>0</mn><mo stretchy="false" form="postfix">}</mo></mrow><annotation encoding="application/x-tex">\{z: \operatorname{Im} z>0\}</annotation></semantics></math>, |
| 233 | +where<br /> |
| 234 | +(a) |
| 235 | +<math role="math" aria-label="A" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>A</mi><annotation encoding="application/x-tex">A</annotation></semantics></math> |
| 236 | +is the complex plane;<br /> |
| 237 | +(b) |
| 238 | +<math role="math" aria-label="A" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>A</mi><annotation encoding="application/x-tex">A</annotation></semantics></math> |
| 239 | +is the unit disc |
| 240 | +<math role="math" aria-label="\{z:|z|<1\}" display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo stretchy="false" form="prefix">{</mo><mi>z</mi><mo>:</mo><mo stretchy="false" form="prefix">|</mo><mi>z</mi><mo stretchy="false" form="prefix">|</mo><mo><</mo><mn>1</mn><mo stretchy="false" form="postfix">}</mo></mrow><annotation encoding="application/x-tex">\{z:|z|<1\}</annotation></semantics></math>.</p> |
| 241 | + |
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