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| 197 | +<h2 class="unnumbered" id="algebra-general-exam">Algebra General |
| 198 | +Exam</h2> |
| 199 | +<ol> |
| 200 | +<li><p>Show (by Sylow theory) that a group of order 72 cannot be simple. |
| 201 | +List all abelian groups of order 72.</p></li> |
| 202 | +<li><p>Let |
| 203 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>G</mi><annotation encoding="application/x-tex">G</annotation></semantics></math> |
| 204 | +be an infinite group containing an element |
| 205 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>x</mi><mo>≠</mo><mn>1</mn></mrow><annotation encoding="application/x-tex">x \neq 1</annotation></semantics></math> |
| 206 | +having only finitely many conjugates. Prove that |
| 207 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>G</mi><annotation encoding="application/x-tex">G</annotation></semantics></math> |
| 208 | +is not simple.</p></li> |
| 209 | +<li><p>Let |
| 210 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mo stretchy="false" form="prefix">(</mo><mi>x</mi><mo stretchy="false" form="postfix">)</mo><mo>=</mo><msup><mi>x</mi><mn>4</mn></msup><mo>−</mo><msup><mi>x</mi><mn>2</mn></msup><mo>−</mo><mn>2</mn><mo>∈</mo><mi>q</mi><mo stretchy="false" form="prefix">[</mo><mi>x</mi><mo stretchy="false" form="postfix">]</mo></mrow><annotation encoding="application/x-tex">f(x)=x^{4}-x^{2}-2 \in q[x]</annotation></semantics></math>. |
| 211 | +Find the splitting field |
| 212 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>F</mi><annotation encoding="application/x-tex">F</annotation></semantics></math> |
| 213 | +of |
| 214 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>f</mi><mo stretchy="false" form="prefix">(</mo><mi>x</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">f(x)</annotation></semantics></math> |
| 215 | +over |
| 216 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>Q</mi><annotation encoding="application/x-tex">Q</annotation></semantics></math>, |
| 217 | +determine its Galois group, and find all subfields of |
| 218 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>F</mi><annotation encoding="application/x-tex">F</annotation></semantics></math>.</p></li> |
| 219 | +<li><p>Let |
| 220 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>k</mi><mo>⊆</mo><mi>K</mi><mo>⊆</mo><mi>L</mi></mrow><annotation encoding="application/x-tex">k \subseteq K \subseteq L</annotation></semantics></math> |
| 221 | +and let |
| 222 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>α</mi><mo>∈</mo><mi>L</mi></mrow><annotation encoding="application/x-tex">\alpha \in L</annotation></semantics></math>. |
| 223 | +Assume that |
| 224 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>K</mi><mi>/</mi><mi>K</mi></mrow><annotation encoding="application/x-tex">K / K</annotation></semantics></math> |
| 225 | +is finite algebraic.<br /> |
| 226 | +(a) Show that |
| 227 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>K</mi><mi>/</mi><mi>K</mi></mrow><annotation encoding="application/x-tex">K / K</annotation></semantics></math> |
| 228 | +separable |
| 229 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>=</mo><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo><mi>/</mi><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">=K(\alpha) / K(\alpha)</annotation></semantics></math> |
| 230 | +separable.<br /> |
| 231 | +(b) Show that |
| 232 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>K</mi><mi>/</mi><mi>K</mi></mrow><annotation encoding="application/x-tex">K / K</annotation></semantics></math> |
| 233 | +normal |
| 234 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mo>⇒</mo><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo><mi>/</mi><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">\Rightarrow K(\alpha) / K(\alpha)</annotation></semantics></math> |
| 235 | +normal.<br /> |
| 236 | +(c) Show that if |
| 237 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>K</mi><mi>/</mi><mi>K</mi></mrow><annotation encoding="application/x-tex">K / K</annotation></semantics></math> |
| 238 | +is Galois, then so is |
| 239 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo><mi>/</mi><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">K(\alpha) / K(\alpha)</annotation></semantics></math> |
| 240 | +and compare the Galois groups |
| 241 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>G</mi><mo stretchy="false" form="prefix">(</mo><mi>K</mi><mi>/</mi><mi>k</mi><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">G(K / k)</annotation></semantics></math> |
| 242 | +and |
| 243 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>G</mi><mo stretchy="false" form="prefix">(</mo><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo><mi>/</mi><mi>K</mi><mo stretchy="false" form="prefix">(</mo><mi>α</mi><mo stretchy="false" form="postfix">)</mo><mo stretchy="false" form="postfix">)</mo></mrow><annotation encoding="application/x-tex">G(K(\alpha) / K(\alpha))</annotation></semantics></math>.</p></li> |
| 244 | +<li><p>What are necessary and sufficient conditions on the commutative |
| 245 | +integral domain |
| 246 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>R</mi><annotation encoding="application/x-tex">R</annotation></semantics></math> |
| 247 | +in order that the polynomial ring in one indeterminate, |
| 248 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>R</mi><mo stretchy="false" form="prefix">[</mo><mi>x</mi><mo stretchy="false" form="postfix">]</mo></mrow><annotation encoding="application/x-tex">R[x]</annotation></semantics></math>, |
| 249 | +be<br /> |
| 250 | +(a) a P.I.D.?<br /> |
| 251 | +(b) a UFD?<br /> |
| 252 | +(c) a Noetherian ring?</p></li> |
| 253 | +<li><p>Let |
| 254 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>R</mi><annotation encoding="application/x-tex">R</annotation></semantics></math> |
| 255 | +be a commutative ring with unit and |
| 256 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>I</mi><annotation encoding="application/x-tex">I</annotation></semantics></math> |
| 257 | +an ideal of |
| 258 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>R</mi><annotation encoding="application/x-tex">R</annotation></semantics></math>. |
| 259 | +Consider the |
| 260 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>R</mi><annotation encoding="application/x-tex">R</annotation></semantics></math>-module |
| 261 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>R</mi><mi>/</mi><mi>I</mi></mrow><annotation encoding="application/x-tex">R / I</annotation></semantics></math>.<br /> |
| 262 | +(a) Show that if |
| 263 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>I</mi><annotation encoding="application/x-tex">I</annotation></semantics></math> |
| 264 | +is a prime ideal, then |
| 265 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>R</mi><mi>/</mi><mi>I</mi></mrow><annotation encoding="application/x-tex">R / I</annotation></semantics></math> |
| 266 | +is indecomposable.<br /> |
| 267 | +(b) Show that |
| 268 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><mi>R</mi><mi>/</mi><mi>I</mi></mrow><annotation encoding="application/x-tex">R / I</annotation></semantics></math> |
| 269 | +is a simple module if and ouly if |
| 270 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>I</mi><annotation encoding="application/x-tex">I</annotation></semantics></math> |
| 271 | +is maximal.</p></li> |
| 272 | +<li><p>Let |
| 273 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>T</mi><annotation encoding="application/x-tex">T</annotation></semantics></math> |
| 274 | +be a linear transformation of |
| 275 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><msup><mi>ℝ</mi><mn>5</mn></msup><annotation encoding="application/x-tex">\mathbb{R}^{5}</annotation></semantics></math> |
| 276 | +having characteristic polynomial |
| 277 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mrow><msup><mi>T</mi><mn>5</mn></msup><mo>−</mo><mi>T</mi></mrow><annotation encoding="application/x-tex">T^{5}-T</annotation></semantics></math>. |
| 278 | +Find its possible rational canonical forms over |
| 279 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>ℝ</mi><annotation encoding="application/x-tex">\mathbb{R}</annotation></semantics></math> |
| 280 | +and its possible Jordan canonical forms over |
| 281 | +<math display="inline" xmlns="http://www.w3.org/1998/Math/MathML"><semantics><mi>ℂ</mi><annotation encoding="application/x-tex">\mathbb{C}</annotation></semantics></math>.</p></li> |
| 282 | +</ol> |
| 283 | + |
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