Chú ý: Để đảm bảo quyền lợi và bảo vệ tài khoản của mình
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{"common":{"save":0,"post_id":"7046","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"4813","post_id":"7046","mon_id":"1158924","chapter_id":"1159147","question":"<p>V\u1edbi <span class=\"math-tex\">$n\\ge1$<\/span> , dãy s\u1ed1 nào sau \u0111ây có d\u1ea1ng khai tri\u1ec3n là <span class=\"math-tex\">$\\dfrac{1}{2};\\dfrac{2}{3};\\dfrac{3}{4};\\dfrac{4}{5};\\dfrac{5}{6};...$<\/span> ?<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$u_n=\\dfrac{n+1}{n}$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$u_n=\\dfrac{n+1}{n+2}$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$u_n=\\dfrac{n}{n+1}$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$u_n=\\dfrac{n+2}{n+1}$<\/span>"],"correct":"3","level":"2","hint":"","answer":"<p>V\u1edbi <span class=\"math-tex\">$n\\ge1$<\/span> , ta có <span class=\"math-tex\">$\\dfrac{1}{2}=\\dfrac{1}{1+1};\\dfrac{2}{3}=\\dfrac{2}{2+1};\\dfrac{3}{4}=\\dfrac{3}{3+1};\\dfrac{4}{5}=\\dfrac{4}{4+1};\\dfrac{5}{6}=\\dfrac{5}{5+1};...$<\/span><\/p><p>nên <span class=\"math-tex\">$u_n=\\dfrac{n}{n+1}$<\/span> .<\/p><p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>C.<\/strong> <span class=\"math-tex\">$u_n=\\dfrac{n}{n+1}$<\/span> .<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-03 02:24:06","option_type":"math","len":0},{"id":"4815","post_id":"7046","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho dãy s\u1ed1 <span class=\"math-tex\">$(u_n)$<\/span> v\u1edbi <span class=\"math-tex\">$u_n=\\dfrac{1}{n.(n+1)}$<\/span> . T\u1ed5ng <span class=\"math-tex\">$u_1+u_2+...+u_{2023}$<\/span> b\u1eb1ng<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$\\dfrac{2023}{2022}$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$\\dfrac{2024}{2023}$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$\\dfrac{2023}{2024}$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$\\dfrac{2022}{2023}$<\/span>"],"correct":"3","level":"2","hint":"","answer":"<p>Ta có <span class=\"math-tex\">$u_n=\\dfrac{1}{n(n+1)}=\\dfrac{1}{n}-\\dfrac{1}{n+1}$<\/span> nên<\/p><p><span class=\"math-tex\">$u_1+u_2+..+u_{2023}$<\/span> <span class=\"math-tex\">$=1-\\dfrac{1}{2}+\\dfrac{1}{2}-\\dfrac{1}{3}+...+\\dfrac{1}{2023}-\\dfrac{1}{2024}$<\/span> <span class=\"math-tex\">$=1-\\dfrac{1}{2024}$<\/span> <span class=\"math-tex\">$=\\dfrac{2023}{2024}$<\/span> .<\/p><p>Ch\u1ecdn C<span style=\"color:#16a085;\"><strong>.<\/strong> <span class=\"math-tex\">$\\dfrac{2023}{2024}$<\/span> .<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-03 02:30:10","option_type":"math","len":0},{"id":"4818","post_id":"7046","mon_id":"1158924","chapter_id":"1159147","question":"<p>Bi\u1ebft dãy s\u1ed1 <span class=\"math-tex\">$(u_n)$<\/span> có các s\u1ed1 h\u1ea1ng \u0111\u1ea7u là <span class=\"math-tex\">$2;6;12;20;30;...$<\/span> . Tìm s\u1ed1 h\u1ea1ng t\u1ed5ng quát c\u1ee7a dãy s\u1ed1 \u0111ó.<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$u_n=n.(n+1)$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$u_n=n.(n+2)$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$u_n=(n+1)^2$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$u_n=4n-2$<\/span>"],"correct":"1","level":"2","hint":"","answer":"<p><span class=\"math-tex\">$u_1=2=1.2=1.(1+1)$<\/span><\/p><p><span class=\"math-tex\">$u_2=6=2.3=2.(2+1)$<\/span><\/p><p><span class=\"math-tex\">$u_3=12=3.4=3.(3+1)$<\/span><\/p><p><span class=\"math-tex\">$u_4=20=4.5=4.(4+1)$<\/span><\/p><p><span class=\"math-tex\">$u_5=30=5.6=5.(5+1)$<\/span><\/p><p>Do \u0111ó <span class=\"math-tex\">$u_n=n.(n+1)$<\/span><\/p><p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>A.<\/strong> <span class=\"math-tex\">$u_n=n.(n+1)$<\/span> .<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-03 02:37:42","option_type":"math","len":0}]}