\u6570\u5b66\u306e\u516c\u5f0f\u306e\u899a\u3048\u65b9\u306f\u300c\u7d75\u300d\u3068\u3057\u3066\u898b\u308b\u306e\u3067\u306f\u306a\u304f(\u753b\u50cf\u8a8d\u8b58\u3067\u306f\u306a\u304f),\u300c\u69cb\u9020\u300d\u3092\u898b\u308b\u3079\u304d\u3067\u3042\u308b\u3002\u4f8b\u3048\u3070, \u30d9\u30af\u30c8\u30eba\u3068\u30d9\u30af\u30c8\u30ebb\u306e\u59cb\u70b9\u3092\u4e00\u81f4\u3055\u305b\u305f\u3068\u304d, 2 \u3064\u306e\u30d9\u30af\u30c8\u30eb\u306e\u7d42\u70b9\u3092\u901a\u308b\u76f4\u7dda\u4e0a\u3092\u6307\u3059\u30d9\u30af\u30c8\u30ebx\u306f,
\n$$\\vec{x}=(1-t)\\vec{a} +t\\vec{b}$$
\n\u306e\u3088\u3046\u306b\u8868\u3055\u308c\u308b\u3002\u3053\u308c\u3092\u4f55\u5341\u56de\u3082\u5531\u3048\u3066\u899a\u3048\u305f\u3068\u3053\u308d\u3067, \u9055\u3046\u8a18\u53f7\u3067\u554f\u984c\u304c\u51fa\u3055\u308c\u305f\u3068\u304d\u306f\u306a\u304b\u306a\u304b\u5bfe\u5fdc\u304c\u3067\u304d\u306a\u3044\u3002\u3053\u3046\u3044\u3046\u5f0f\u306f, a \u3068 b \u306e\u4fc2\u6570 1-t, t \u304c\u300c\u548c\u304c1\u3067\u3042\u308b\u300d\u3053\u3068\u3092\u898b\u629c\u304d, \u300c\u548c\u304c 1 \u3067\u3042\u308b\u4fc2\u6570\u3067\u8868\u3055\u308c\u308b\u300d\u3068\u8a8d\u8b58\u3059\u3079\u304d\u3067\u3042\u308b\u3002\u305d\u3046\u3067\u306a\u3044\u3068, \u300c\u610f\u5473\u306e\u5206\u304b\u3089\u306a\u3044\u3067\u6697\u8a18\u3055\u3048\u3059\u308c\u3070\u3088\u3044\u300d\u3068\u306a\u308b\u3002\u3042\u305f\u304b\u3082\u546a\u6587\u3092\u5531\u3048\u308b\u3088\u3046\u306b\u3002\u3053\u308c\u306f\u6570\u5b66\u306e\u6559\u80b2\u3067\u306f\u306a\u3044\u3002<\/p>\n
\u3055\u3066, \u6559\u79d1\u66f8\u306e\u4e2d\u306b\u4f1d\u7d71\u7684\u306b\u305d\u308c\u306b\u8fd1\u3044\u3068\u3053\u308d\u304c\u3042\u308b\u3002\u305d\u308c\u306f, \u6570\u5b66I\u306e\u4e09\u89d2\u6bd4\u306e\u4f59\u5f26\u5b9a\u7406\u306e\u90e8\u5206\u3067\u3042\u308b\u3002
\n\u4e09\u89d2\u5f62 ABC \u306b\u304a\u3044\u3066 BC=a, CA=b, AB=c \u3068\u3059\u308b\u3068\u304d,
\n(1)\u3000$$a^2 =b^2+c^2 -2bc \\cos A$$
\n\u304c\u4f59\u5f26\u5b9a\u7406\u3067\u3042\u308b\u304c, \u307b\u3068\u3093\u3069\u306e\u6559\u79d1\u66f8\u306b\u306f, \u4e0a\u8a18\u306e\u4ed6\u306b
\n(2)\u3000$$b^2 =c^2+a^2 -2ca \\cos B$$
\n(3)\u3000$$c^2 =a^2+b^2 -2ab \\cos C$$
\n\u304c\u66f8\u304b\u308c\u3066\u3042\u308b\u3002\u3053\u308c\u306f\u610f\u5473\u304c\u306a\u3044\u3002\u3068\u3044\u3046\u3088\u308a\u3082, 3 \u672c\u66f8\u304f\u3053\u3068\u306f\u3080\u3057\u308d\u5bb3\u3067\u3042\u308b\u3002
\n\u751f\u5f92\u306f, \u3053\u306e 3 \u672c\u306e\u5f0f\u3092\u899a\u3048\u3088\u3046\u3068\u3059\u308b\u3060\u308d\u3046\u3002\u3057\u304b\u3057, 3 \u672c\u899a\u3048\u3066\u3082\u4e09\u89d2\u5f62\u306e 3 \u8fba\u306e\u9577\u3055\u304c a, b, c \u3067\u306f\u306a\u304f p, q, r \u3067\u3042\u308c\u3070\u4f7f\u3048\u306a\u3044\u3002\u3082\u3057\u3082,
\n\u300c(1) \u306e a, b, c \u306e\u90e8\u5206\u3092 p, q, r \u306b\u5f53\u3066\u306f\u3081\u308c\u3070\u3088\u3044\u300d
\n\u3068\u3044\u3046\u306e\u3067\u3042\u308c\u3070, \u6700\u521d\u304b\u3089 (2), (3) \u306a\u3069\u306a\u3044\u65b9\u304c\u3088\u3044\u3002
\n(2) \u3068 (3) \u306e\u5b58\u5728\u306f, \u6570\u5b66\u6559\u80b2\u306e\u7acb\u5834\u304b\u3089\u3059\u308c\u3070\u7121\u7528\u306e\u9577\u7269\u3067\u3042\u308b\u3002\u3057\u304b\u3057, \u4f55\u5341\u5e74\u3082\u6559\u79d1\u66f8\u306b\u306f\u3053\u306e 3 \u672c\u304c\u66f8\u304b\u308c\u308b\u3002
\n\u3082\u3057\u304b\u3059\u308b\u3068, \u6b63\u5f26\u5b9a\u7406\u3068\u306e\u8a18\u8ff0\u306e\u517c\u306d\u5408\u3044\u304c\u3042\u308b\u306e\u304b\u3082\u3057\u308c\u306a\u3044\u304c, \u6b63\u5f26\u5b9a\u7406\u306f\u6b63\u5f26\u5b9a\u7406\u3067\u4eca\u306e\u72b6\u6cc1\u3068\u306f\u5c11\u3057\u7570\u306a\u308b\u3002
\n\u6559\u79d1\u66f8\u306b\u304a\u3044\u3066\u306f, \u4e09\u89d2\u5f62\u306e\u9762\u7a4d\u3082
\n$$S=\\frac{1}{2} bc \\sin A =\\frac{1}{2} ca \\sin B =\\frac{1}{2} ab \\sin C$$
\n\u304c\u66f8\u304b\u308c\u3066\u3044\u305f\u308a, $$\\cos A=\\frac{(b^2+c^2-a^2)}{2bc}$$ \u3082 3 \u901a\u308a\u66f8\u304b\u308c\u3066\u3044\u305f\u308a\u3059\u308b\u3002
\n\u3053\u308c\u3082\u610f\u5473\u304c\u306a\u3044\u306e\u3060\u304c\u3001\u4f1d\u7d71\u7684\u306a\u8a18\u8ff0\u3067\u3042\u308b\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u6570\u5b66\u306e\u516c\u5f0f\u306e\u899a\u3048\u65b9\u306f\u300c\u7d75\u300d\u3068\u3057\u3066\u898b\u308b\u306e\u3067\u306f\u306a\u304f(\u753b\u50cf\u8a8d\u8b58\u3067\u306f\u306a\u304f),\u300c\u69cb\u9020\u300d\u3092\u898b\u308b\u3079\u304d\u3067\u3042\u308b\u3002\u4f8b\u3048\u3070, \u30d9\u30af\u30c8\u30eba\u3068\u30d9\u30af\u30c8\u30ebb\u306e\u59cb\u70b9\u3092\u4e00\u81f4\u3055\u305b\u305f\u3068\u304d, 2 \u3064\u306e\u30d9\u30af\u30c8\u30eb\u306e\u7d42\u70b9\u3092\u901a\u308b\u76f4\u7dda\u4e0a\u3092\u6307\u3059\u30d9\u30af\u30c8\u30ebx\u306f, $$\\vec […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[7,4],"tags":[],"class_list":["post-1327","post","type-post","status-publish","format-standard","hentry","category-7","category-4"],"_links":{"self":[{"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1327","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=1327"}],"version-history":[{"count":4,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1327\/revisions"}],"predecessor-version":[{"id":1357,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=\/wp\/v2\/posts\/1327\/revisions\/1357"}],"wp:attachment":[{"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=1327"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=1327"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/math.co.jp\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=1327"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}