{"id":2296,"date":"2025-12-24T17:18:41","date_gmt":"2025-12-24T08:18:41","guid":{"rendered":"https:\/\/math-travel.com\/?p=2296"},"modified":"2026-02-11T16:28:25","modified_gmt":"2026-02-11T07:28:25","slug":"sine-theorem","status":"publish","type":"post","link":"https:\/\/math-travel.jp\/math-1\/sine-theorem\/","title":{"rendered":"\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u3068\u4f7f\u3044\u9053\u3092\u5fb9\u5e95\u89e3\u8aac\uff01\u300c\u3044\u3064\u4f7f\u3046\uff1f\u300d\u304c\u308f\u304b\u308b\u5224\u65ad\u57fa\u6e96\u3092\u4f1d\u6388"},"content":{"rendered":"\n
\u6570\u5b66\u2160\u4e09\u89d2\u6bd4\u306e\u306a\u304b\u3067\u591a\u304f\u306e\u9ad8\u6821\u751f\u3092\u82e6\u3057\u3081\u308b\u306e\u304c\u300c\u6b63\u5f26\u5b9a\u7406\u300d<\/span>\u3067\u3059\u3002<\/span><\/p>\n\n\n\n \u300c\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u3092\u5fd8\u308c\u3066\u3057\u307e\u3063\u305f\u300d <\/p>\n\n\n\n \u300c\u6b63\u5f26\u5b9a\u7406\u306e\u4f7f\u3044\u65b9\u304c\u5206\u304b\u3089\u306a\u3044\u300d<\/p>\n<\/div><\/div>\n\n\n\n \u4eca\u56de\u306f\u6b63\u5f26\u5b9a\u7406\u306b\u95a2\u3059\u308b\u3053\u3093\u306a\u60a9\u307f\u3092\u89e3\u6c7a\u3057\u307e\u3059\u3002<\/p>\n\n\n \u6b63\u5f26\u5b9a\u7406\u304c\u3088\u304f\u5206\u304b\u3089\u306a\u304f\u3066\u2026<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n\n \u4eca\u56de\u306f\u4e09\u89d2\u6bd4\u306e\u6b63\u5f26\u5b9a\u7406\u306b\u3064\u3044\u3066\u89e3\u8aac\u3057\u3066\u3044\u304d\u307e\u3059\u3002<\/span><\/p>\n\n\n\n \u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092R\u3068\u3059\u308b\u3068\u3001\u6b21\u304c\u6210\u308a\u7acb\u3064\u3002<\/p>\n\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=\\frac{b}{\\sin B}=\\frac{c}{\\sin C}=2R\\]<\/p>\n<\/div><\/div>\n\n\n\n \u3055\u3063\u305d\u304f\u3067\u3059\u304c\u4e0b\u306e\u4e09\u89d2\u5f62ABC\u3092\u307f\u3066\u3001\u8fbaAB\u306e\u9577\u3055\u304c\u5206\u304b\u308a\u307e\u3059\u304b\uff1f<\/p>\n\n\n \u300c\u3053\u308c\u3060\u3051\u3058\u3083\u5206\u304b\u3089\u306a\u3044\u3088\uff01\u300d<\/span><\/p>\n\n\n\n \u3053\u3046\u601d\u3063\u305f\u65b9\u306f\u6b63\u5f26\u5b9a\u7406\u3092\u4f7f\u3044\u3053\u306a\u305b\u3066\u3044\u306a\u3044\u306e\u3067\u8981\u6ce8\u610f\u3067\u3059\uff01<\/span><\/p>\n\n\n\n \u5b9f\u306f”\u6b63\u5f26\u5b9a\u7406”\u3092\u4f7f\u3046\u3053\u3068\u3067\u4e09\u89d2\u5f62\u306e\u8fba\u306e\u9577\u3055\u3084\u89d2\u306e\u5927\u304d\u3055\u3092\u7c21\u5358\u306b\u6c42\u3081\u308b\u3053\u3068\u304c\u3067\u304d\u308b\u306e\u3067\u3059\uff01<\/span><\/p>\n\n\n\n \u4eca\u56de\u306f\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u3084\u4f7f\u3044\u65b9<\/span>\u306b\u3064\u3044\u3066\u8a18\u4e8b\u3092\u66f8\u3044\u305f\u306e\u3067\u305c\u3072\u6700\u5f8c\u307e\u3067\u3054\u89a7\u304f\u3060\u3055\u3044\u3002<\/p>\n\n\n \u6c17\u306b\u306a\u308b\u898b\u51fa\u3057\u3092\u30af\u30ea\u30c3\u30af\u3057\u3066\u3001 \u5404\u9802\u70b9A,B,C\u3068\u3057\u3066\u3001\u5411\u304b\u3044\u5408\u3046\u8fba\u3092a,b,c\u3068\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=\\frac{b}{\\sin B}=\\frac{c}{\\sin C}=2R\\]<\/p>\n<\/div><\/div>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3092\u6d3b\u7528\u3059\u308b\u3053\u3068\u3067\u3001\u8fba\u3084\u89d2\u306e\u5927\u304d\u3055\u3092\u6c42\u3081\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n \u516c\u5f0f\u306f\u899a\u3048\u3066\u308b\u3051\u3069\u4f7f\u3044\u65b9\u304c\u3088\u304f\u5206\u304b\u3089\u306a\u304f\u3066\u2026<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n \u4f8b\u984c\u3092\u3082\u3068\u306b\u6b63\u5f26\u5b9a\u7406\u3092\u4f7f\u3063\u3066\u307f\u3088\u3046\uff01<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n\n \u4ee5\u4e0b\u306e\u554f\u984c\u3092\u4f8b\u306b\u3057\u3066\u6b63\u5f26\u5b9a\u7406\u306e\u4f7f\u3044\u65b9\u3092\u89e3\u8aac\u3057\u307e\u3059\u3002<\/p>\n\n\n\n \u534a\u5f845cm\u306e\u5186\u306b\u5185\u63a5\u3059\u308b\u4e09\u89d2\u5f62ABC\u304c\u3042\u308a\u307e\u3059\u3002<\/p>\n\n\n\n \\(C=60^\\circ\\)\u306e\u3068\u304d\u3001\u8fbaAB\u306e\u5024\u3092\u6c42\u3081\u3088\u3046\u3002<\/p>\n\n\n\n \u4e0a\u306e\u554f\u984c\u3067\u306f\u5186\u306e\u534a\u5f84\u3068\u89d2\u306e\u5927\u304d\u3055\u304c\u5206\u304b\u3063\u3066\u3044\u308b\u306e\u3067\u3001\u6b63\u5f26\u5b9a\u7406\u3092\u7528\u3044\u3066\u8003\u3048\u307e\u3059\u3002<\/p>\n\n\n\n \u8fbaAB\u306e\u5927\u304d\u3055\u3092c\u3068\u3059\u308b\u3068\u6b63\u5f26\u5b9a\u7406\u3088\u308a\u3001<\/p>\n\n\n\n \\begin{eqnarray} \u3057\u305f\u304c\u3063\u3066\u3001AB\u306e\u5927\u304d\u3055\u306f\\(5\\sqrt{3}\\)\u3060\u3068\u5206\u304b\u308a\u307e\u3057\u305f\u3002<\/p>\n\n\n\n \u306a\u305c\u6b63\u5f26\u5b9a\u7406\u304c\u6210\u308a\u7acb\u3064\u306e\u304b\u8a3c\u660e\u3057\u3066\u3044\u304d\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\n \u8a3c\u660e\u306e\u65b9\u91dd\u3068\u3057\u3066\u306f\u3001\u89d2A\u306e\u5927\u304d\u3055\u3092\u5834\u5408\u5206\u3051<\/span>\u3057\u3066\u8003\u3048\u307e\u3059\u3002<\/p>\n\n\n\n \u4e09\u89d2\u5f62\u306e\uff13\u3064\u306e\u9802\u70b9\u3092\u901a\u3059\u5186\u3092\u3001\u305d\u306e\u4e09\u89d2\u5f62\u306e\u5916\u63a5\u5186<\/span>\u3068\u3044\u3044\u307e\u3059\u3002<\/p>\n\n\n\n \u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092R\u3068\u3057\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n \u70b9A\u3068\u306f\u7570\u306a\u308b\u70b9D\u3092\u5186\u5468\u4e0a\u306b\u3068\u308a\u3001\u76f4\u89d2\u4e09\u89d2\u5f62\\(DCB\\)\u3092\u4f5c\u308a\u307e\u3059\u3002<\/p>\n\n\n\n \u5186\u5468\u89d2\u3068\u4e2d\u5fc3\u89d2\u306e\u6027\u8cea\u306b\u3088\u308a\u3001<\/p>\n\n\n\n \\[\\angle BDC = \\angle BAC \\]<\/p>\n\n\n\n \u307e\u305f\u3001\\(\\angle BCD = 90^\\circ\\)\u3088\u308a\u3001<\/p>\n\n\n\n \\[BD=2R\\]<\/p>\n\n\n\n \u25b3BCD\u306b\u304a\u3044\u3066<\/p>\n\n\n\n \\begin{eqnarray} \u304c\u6210\u308a\u7acb\u3064\u3002<\/p>\n\n\n\n \u3057\u305f\u304c\u3063\u3066\u3001<\/p>\n\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=2R\\]<\/p>\n\n\n\n \u8fbaBC\u306f\u3001\u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u76f4\u5f84\u306b\u306a\u306e\u3067<\/p>\n\n\n\n \\[a=2R\\]<\/p>\n\n\n\n \u4e00\u65b9\u3067\u3001\\(\\sin A=\\sin 90^\\circ=1\\)\u306a\u306e\u3067\u3001<\/p>\n\n\n\n \\[a=2R\\sin A\\]<\/p>\n\n\n\n \u3057\u305f\u304c\u3063\u3066\u3001<\/p>\n\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=2R\\]<\/p>\n\n\n\n \u4e0a\u306e\u56f3\u3067\u3001\u7dda\u5206BD\u306f\u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u76f4\u5f84\u3068\u3059\u308b\u3002<\/p>\n\n\n\n \\(\\angle BDC=D\\)\u3068\u3059\u308b\u3068\u3001\u5186\u5468\u89d2\u3068\u4e2d\u5fc3\u89d2\u306e\u6027\u8cea\u3088\u308a<\/p>\n\n\n\n \\[2A+2D=360^\\circ\\]<\/p>\n\n\n\n \u3059\u306a\u308f\u3061\u3001<\/p>\n\n\n\n \\[A+D=180^\\circ\\]<\/p>\n\n\n\n \\begin{eqnarray} \u3053\u3053\u3067\u3001<\/p>\n\n\n\n \\(\\angle BCD=90^\\circ\u3001BD=2R\\)\u3067\u3042\u308b\u304b\u3089\u3001\u25b3BCD\u306b\u304a\u3044\u3066\u3001<\/p>\n\n\n\n \\begin{eqnarray} \u3057\u305f\u304c\u3063\u3066\u3001<\/p>\n\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=2R\\]<\/p>\n\n\n\n [1]~[3]\u3088\u308a\u3001\u6b63\u5f26\u5b9a\u7406\u306e\u8a3c\u660e\u7d42\u4e86\u3002<\/p>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3068\u3042\u308f\u305b\u3066\u899a\u3048\u3066\u304a\u304d\u305f\u3044\u306e\u304c\u4f59\u5f26\u5b9a\u7406<\/span>\u3067\u3059\u3002<\/p>\n\n\n\n \u4e09\u89d2\u5f62ABC\u306e\u5411\u304b\u3044\u5408\u3046\u8fba\u3092a,b,c\u3068\u3059\u308b\u3068\u3001<\/p>\n\n\n \u25b3ABC\u306b\u304a\u3044\u3066\u3001\u6b21\u304c\u6210\u308a\u7acb\u3064\u3002<\/p>\n\n\n\n \\begin{eqnarray} \u540d\u524d\u306e\u4f3c\u3066\u3044\u308b2\u3064\u306e\u5b9a\u7406\u3067\u3059\u304c\u3001\u4f7f\u3044\u5206\u3051\u306b\u56f0\u308b\u3053\u3068\u304c\u3042\u308b\u306f\u305a\u3067\u3059\u3002<\/p>\n\n\n\n \u305d\u308c\u305e\u308c\u306e\u5b9a\u7406\u3092\u4f7f\u3046\u30bf\u30a4\u30df\u30f3\u30b0\u3092\u3056\u3063\u304f\u308a\u3068\u307e\u3068\u3081\u307e\u3057\u305f\u3002\u3042\u304f\u307e\u3067\u53c2\u8003\u7a0b\u5ea6\u306b\u3054\u89a7\u304f\u3060\u3055\u3044\u3002<\/p>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3092\u4f7f\u3046\u6642<\/p>\n\n\n\n \u24601\u8fba\u30682\u3064\u306e\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408 \u4f59\u5f26\u5b9a\u7406\u3092\u4f7f\u3046\u6642<\/p>\n\n\n\n \u24602\u8fba\u3068\u305d\u306e\u9593\u306e\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408 \u300c5\u3064\u3082\u899a\u3048\u3089\u308c\u306a\u3044\u3088\uff01\u300d<\/p>\n\n\n\n \u305d\u3093\u306a\u65b9\u306f\u4ee5\u4e0b\u306e\u3088\u3046\u306b\u899a\u3048\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\n \u8fba\u3088\u308a\u3082\u89d2\u306e\u60c5\u5831\u304c\u591a\u3044\u3000\u21d2\u3000\u6b63\u5f26\u5b9a\u7406 \u3053\u308c\u306a\u3089\u899a\u3048\u3084\u3059\u3044\u3067\u3059\uff01\uff01<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n \u5fc5\u305a\u4f7f\u3048\u308b\u308f\u3051\u3067\u306f\u306a\u3044\u306e\u3067\u3001\u53c2\u8003\u7a0b\u5ea6\u306b\u4f7f\u3063\u3066\u306d<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n\n \u4eca\u56de\u5b66\u3093\u3060\u6b63\u5f26\u5b9a\u7406\u3092\u7528\u3044\u3066\u3001\u7df4\u7fd2\u554f\u984c\u306b\u6311\u6226\u3057\u3066\u307f\u307e\u3057\u3087\u3046\u3002<\/p>\n\n\n\n \\(a=5,A=45^\\circ\\)\u306e\u4e09\u89d2\u5f62ABC\u306b\u304a\u3044\u3066\u3001\u5916\u63a5\u5186\u306e\u534a\u5f84\\(R\\)\u3092\u6c42\u3081\u3088\u3046\u3002<\/p>\n\n\n\n \u89e3\u8aac<\/span><\/p>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3088\u308a\u3001<\/p>\n\n\n\n \\begin{eqnarray} \u3057\u305f\u304c\u3063\u3066\u3001<\/p>\n\n\n\n \\[\\displaystyle R=\\frac{5\\sqrt{2}}{2}\\]<\/p>\n\n\n\n \\(\u25b3ABC\\)\u306b\u304a\u3044\u3066\\(c=10\\)\u3067\u3001\u5916\u63a5\u5186\u306e\u534a\u5f84\u304c\\(R=10\\)\u306e\u3068\u304d\u3001\\(\\angle C\\)\u306e\u5927\u304d\u3055\u3092\u6c42\u3081\u3088\u3046\u3002<\/p>\n<\/div><\/div>\n\n\n\n \u89e3\u8aac<\/span><\/p>\n\n\n\n \u6b63\u5f26\u5b9a\u7406<\/p>\n\n\n\n \\begin{eqnarray} \u3057\u305f\u304c\u3063\u3066\u3001<\/p>\n\n\n\n \\[\\angle C=30^\\circ,150^\\circ\\]<\/p>\n\n\n \u6b63\u5f26\u5b9a\u7406\u304c\u4f7f\u3048\u308b\u3088\u3046\u306b\u306a\u308a\u307e\u3057\u305f\uff01<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n\n \u4eca\u56de\u306f\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u306b\u3064\u3044\u3066\u307e\u3068\u3081\u307e\u3057\u305f\u3002<\/span><\/p>\n\n\n \u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092R\u3068\u3059\u308b\u3068\u3001\u6b21\u304c\u6210\u308a\u7acb\u3064\u3002<\/p>\n\n\n\n \\[\\displaystyle \\frac{a}{\\sin A}=\\frac{b}{\\sin B}=\\frac{c}{\\sin C}=2R\\]<\/p>\n<\/div><\/div>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3092\u4f7f\u3046\u3053\u3068\u3067\u3001\u8fba\u306e\u9577\u3055\u3084\u89d2\u306e\u5927\u304d\u3055\u3092\u6c42\u3081\u308b\u3053\u3068\u304c\u3067\u304d\u307e\u3059\u3002<\/p>\n\n\n\n \u6b63\u5f26\u5b9a\u7406\u3092\u4f7f\u3046\u6642<\/p>\n\n\n\n \u24601\u8fba\u30682\u3064\u306e\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408 \u4f59\u5f26\u5b9a\u7406\u3092\u4f7f\u3046\u6642<\/p>\n\n\n\n \u24602\u8fba\u3068\u305d\u306e\u9593\u306e\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408 \u4e09\u89d2\u95a2\u6570\u306b\u306f\u91cd\u8981\u306a\u516c\u5f0f<\/span>\u304c\u305f\u304f\u3055\u3093\u3042\u308a\u307e\u3059\u3002<\/p>\n","protected":false},"excerpt":{"rendered":" \u6570\u5b66\u2160\u4e09\u89d2\u6bd4\u306e\u306a\u304b\u3067\u591a\u304f\u306e\u9ad8\u6821\u751f\u3092\u82e6\u3057\u3081\u308b\u306e\u304c\u300c\u6b63\u5f26\u5b9a\u7406\u300d\u3067\u3059\u3002 \u4eca\u56de\u306f\u6b63\u5f26\u5b9a\u7406\u306b\u95a2\u3059\u308b\u3053\u3093\u306a\u60a9\u307f\u3092\u89e3\u6c7a\u3057\u307e\u3059\u3002 \u4eca\u56de\u306f\u4e09\u89d2\u6bd4\u306e\u6b63\u5f26\u5b9a\u7406\u306b\u3064\u3044\u3066\u89e3\u8aac\u3057\u3066\u3044\u304d\u307e\u3059\u3002 \u3055\u3063\u305d\u304f\u3067\u3059\u304c\u4e0b\u306e\u4e09\u89d2\u5f62ABC\u3092\u307f\u3066\u3001\u8fbaAB\u306e\u9577\u3055\u304c\u5206\u304b […]<\/p>\n","protected":false},"author":1,"featured_media":10823,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"swell_btn_cv_data":"","footnotes":""},"categories":[34,222],"tags":[33,37,10,11],"class_list":["post-2296","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-sankakuhi","category-math-1","tag-33","tag-37","tag-a","tag-11"],"yoast_head":"\n
\u9ad8\u6821\u751f<\/span><\/div>
<\/figure>\n<\/div>\n\n\n
\u30b7\u30fc\u30bf<\/span><\/div>
\u305c\u3072\u6700\u5f8c\u307e\u3067\u3054\u89a7\u304f\u3060\u3055\u3044\u3002<\/p>\n<\/span><\/span><\/span><\/div><\/div><\/div><\/div>\n\n\n\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f<\/h2>\n\n\n
<\/figure>\n<\/div>\n\n\n
\u6b63\u5f26\u5b9a\u7406\u306f\u4e09\u89d2\u6bd4\u306e\u91cd\u8981\u306a\u516c\u5f0f\u306e1\u3064<\/span>\u3067\u3059\u3002<\/span><\/p>\n\n\n\n
<\/figure>\n<\/div>\n\n\n
\u25b3ABC\u306e\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092R\u3068\u3059\u308b\u3068\u3001\u6b21\u304c\u6210\u308a\u7acb\u3064\u3002<\/p>\n\n\n\n
\u9ad8\u6821\u751f<\/span><\/div>
\u30b7\u30fc\u30bf<\/span><\/div>\u6b63\u5f26\u5b9a\u7406\u306e\u4f7f\u3044\u65b9<\/h2>\n\n\n\n
<\/p>\n<\/div><\/div>\n\n\n\n
\\displaystyle \\frac{c}{\\sin C}&=&2R\\\\
\\displaystyle \\frac{c}{\\sin 60^\\circ}&=&2 \\times 5\\\\
c&=&10 \\sin 60^\\circ\\\\
c&=&5\\sqrt{3}
\\end{eqnarray}<\/p>\n\n\n\n\u6b63\u5f26\u5b9a\u7406\u306e\u8a3c\u660e<\/h2>\n\n\n\n
\\([1]\u30000^\\circ < A < 90^\\circ\\)\u306e\u3068\u304d<\/h3>\n\n\n\n
<\/figure>\n<\/div>\n\n\n
a&=&2R\\sin \\angle BDC\\\\
&=&2R\\sin \\angle BAC
\\end{eqnarray}<\/p>\n\n\n\n\\([2]\u3000A = 90^\\circ\\)\u306e\u3068\u304d<\/h3>\n\n\n
<\/figure>\n<\/div>\n\n\n\\([3]\u300090^\\circ < A < 180^\\circ\\)\u306e\u3068\u304d<\/h3>\n\n\n
<\/figure>\n<\/div>\n\n\n
\\sin D&=&\\sin(180^\\circ -A)\\\\
&=&\\sin A
\\end{eqnarray}<\/p>\n\n\n\n
a&=&2R\\sin D\\\\
&=&2R \\sin (180^\\circ -A)\\\\
&=&2R \\sin A
\\end{eqnarray}<\/p>\n\n\n\n\u4f59\u5f26\u5b9a\u7406\u3068\u306e\u4f7f\u3044\u5206\u3051<\/h2>\n\n\n\n
<\/figure>\n<\/div>\n\n\n
a^{2}=b^{2}+c^{2}-2bc \\cos A\\\\
b^{2}=a^{2}+c^{2}-2ac \\cos B\\\\
c^{2}=a^{2}+b^{2}-2ab \\cos C
\\end{eqnarray}<\/p>\n<\/div><\/div>\n\n\n\n
\u24611\u7d44\u306e\u5411\u304b\u3044\u5408\u3046\u8fba\u3068\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408
\u2462\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092\u6c42\u3081\u305f\u3044\u5834\u5408<\/p>\n\n\n\n
\u24613\u8fba\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u3068\u304d<\/p>\n<\/div><\/div>\n\n\n\n
\u89d2\u3088\u308a\u3082\u8fba\u306e\u60c5\u5831\u304c\u591a\u3044\u3000\u21d2\u3000\u4f59\u5f26\u5b9a\u7406<\/p>\n\n\n
\u9ad8\u6821\u751f<\/span><\/div>
\u30b7\u30fc\u30bf<\/span><\/div>\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u300a\u7df4\u7fd2\u554f\u984c\u300b<\/h2>\n\n\n\n
<\/p>\n<\/div><\/div>\n\n\n\n
\\displaystyle 2R&=&\\frac{a}{sin A}\\\\
\\displaystyle &=&\\frac{5}{sin 45^\\circ}\\\\
\\displaystyle &=&\\frac{5}{\\frac{1}{\\sqrt{2}}}\\\\
&=&5\\sqrt{2}
\\end{eqnarray}<\/p>\n\n\n\n
\\displaystyle \\frac{c}{sin C}&=&2R\\\\
\\displaystyle \\frac{10}{sin C}&=&20\\\\
\\displaystyle sin C=\\frac{1}{2}
\\end{eqnarray}<\/p>\n\n\n\n
\u9ad8\u6821\u751f<\/span><\/div>\u6b63\u5f26\u5b9a\u7406\u306e\u516c\u5f0f\u3000\u307e\u3068\u3081<\/h2>\n\n\n\n
<\/figure>\n<\/div>\n\n\n
\u24611\u7d44\u306e\u5411\u304b\u3044\u5408\u3046\u8fba\u3068\u89d2\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u5834\u5408
\u2462\u5916\u63a5\u5186\u306e\u534a\u5f84\u3092\u6c42\u3081\u305f\u3044\u5834\u5408<\/p>\n\n\n\n
\u24613\u8fba\u304c\u4e0e\u3048\u3089\u308c\u3066\u3044\u308b\u3068\u304d<\/p>\n<\/div><\/div>\n\n\n\n