{"trustable":false,"prependHtml":"\u003cscript\u003e window.katexOptions \u003d { disable: true }; \u003c/script\u003e\n\u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {\n inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027], [\u0027$\u0027,\u0027$\u0027]],\n displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027], [\u0027$$\u0027,\u0027$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS-MML_HTMLorMML\" type\u003d\"text/javascript\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"我们有一个特殊的凸多边形,这个多边形上的每个点到原点的距离都相同,都是d。\u003cbr\u003e\n现在用n条线段将原点和每个凸多边形顶点连接起来,每对相邻的线段有一个夹角。\u003cbr\u003e\n现在给你关于角度的数据,要求你计算该凸多边形的面积。"}},{"title":"Input","value":{"format":"HTML","content":"多组输入\n每组数据第一行给定n和d,表示凸多边形顶点的数量和顶点与原点的距离d,(3 \u0026lt;\u003d N \u0026lt;\u003d 10, 1 \u0026lt;\u003d D \u0026lt;\u003d 10)\u003cbr\u003e\n下一行给定n个整数,分别表示相邻连线的夹角,显然n个夹角的总和一定会是360。\n\u003cbr\u003e"}},{"title":"Output","value":{"format":"HTML","content":"对于每组数据,输出凸多边形的面积,精确到小数点后三位。\n\u003cbr\u003e"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cpre\u003e4 1\n90 90 90 90\n6 1\n60 60 60 60 60 60\u003c/pre\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cpre\u003e2.000\n2.598\u003c/pre\u003e"}}]}