{"common":{"save":0,"post_id":"7054","level":1,"total":10,"point":10,"point_extra":0},"segment":[{"id":"4911","post_id":"7054","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho d&atilde;y s\u1ed1&nbsp;<span class=\"math-tex\">$(u_n)$<\/span>&nbsp;\u0111\u01b0\u1ee3c x&aacute;c \u0111\u1ecbnh b\u1edfi&nbsp;<span class=\"math-tex\">$u_1=\\dfrac{1}{3}$<\/span>&nbsp;v&agrave;&nbsp;<span class=\"math-tex\">$u_n=3u_{n-1}$<\/span>&nbsp;v\u1edbi m\u1ecdi&nbsp;<span class=\"math-tex\">$n\\ge2$<\/span>. S\u1ed1 h\u1ea1ng th\u1ee9 n\u0103m c\u1ee7a d&atilde;y s\u1ed1&nbsp;<span class=\"math-tex\">$(u_n)$<\/span>&nbsp;l&agrave;<\/p>","options":["<strong>A.<\/strong> 27","<strong>B.<\/strong> 9","<strong>C.<\/strong> 81","<strong>D.<\/strong> 243"],"correct":"1","level":"1","hint":"","answer":"<p>Ta c&oacute;&nbsp;<span class=\"math-tex\">$u_2=3u_1=3.\\dfrac{1}{3}=1$<\/span>&nbsp;;&nbsp;<span class=\"math-tex\">$u_3=3u_2=3.1=3$<\/span><\/p><p><span class=\"math-tex\">$u_4=3u_3=3.3=9$<\/span>&nbsp;;&nbsp;<span class=\"math-tex\">$u_5=3u_4=3.9=27$<\/span>&nbsp;<\/p><p>V\u1eady s\u1ed1 h\u1ea1ng th\u1ee9 n\u0103m c\u1ee7a d&atilde;y s\u1ed1 l&agrave; 27.<\/p><p>Ch\u1ecdn&nbsp; &nbsp;<span style=\"color:#16a085;\"><strong>A.<\/strong> 27.<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-13 01:17:48","option_type":"txt","len":0},{"id":"4912","post_id":"7054","mon_id":"1158924","chapter_id":"1159147","question":"<p>Trong c&aacute;c d&atilde;y s\u1ed1 sau, d&atilde;y s\u1ed1 n&agrave;o l&agrave; c\u1ea5p s\u1ed1 c\u1ed9ng?<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$21 ; -3 ; -27 ; -51 ; -75$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$\\dfrac{1}{2};\\dfrac{5}{4};2;\\dfrac{11}{4};\\dfrac{15}{4}$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$\\sqrt{1};\\sqrt{2};\\sqrt{3};\\sqrt{4};\\sqrt{5}$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$\\dfrac{1}{20};\\dfrac{1}{30};\\dfrac{1}{40} ; \\dfrac{1}{50};\\dfrac{1}{60}$<\/span>"],"correct":"1","level":"1","hint":"","answer":"<p>X&eacute;t \u0111&aacute;p &aacute;n<strong> A<\/strong>, ta th\u1ea5y<\/p><p><span class=\"math-tex\">$u_2-u_1=-3-21=-24$<\/span><\/p><p><span class=\"math-tex\">$u_3-u_2=-27-(-3)=-24$<\/span><\/p><p><span class=\"math-tex\">$u_4-u_3=-51-(-27)=-24$<\/span><\/p><p><span class=\"math-tex\">$u_5-u_4=-75-(-51)=-24$<\/span><\/p><p>V\u1eady d&atilde;y&nbsp;&nbsp;&nbsp;<span class=\"math-tex\">$21 ; -3 ; -27 ; -51 ; -75$<\/span>&nbsp; l&agrave; c\u1ea5p s\u1ed1 c\u1ed9ng.<\/p><p>Ch\u1ecdn&nbsp; &nbsp;&nbsp;<span style=\"color:#16a085;\"><strong>A.<\/strong> <span class=\"math-tex\">$21 ; -3 ; -27 ; -51 ; -75$<\/span>.<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-13 01:24:21","option_type":"math","len":0},{"id":"4915","post_id":"7054","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho c\u1ea5p s\u1ed1 c\u1ed9ng&nbsp;<span class=\"math-tex\">$(u_n)$<\/span>&nbsp;c&oacute; s\u1ed1 h\u1ea1ng \u0111\u1ea7u&nbsp;<span class=\"math-tex\">$u_1=-5$<\/span>, c&ocirc;ng sai&nbsp;<span class=\"math-tex\">$d=4$<\/span>. C&ocirc;ng th\u1ee9c c\u1ee7a s\u1ed1 h\u1ea1ng t\u1ed5ng qu&aacute;t&nbsp;<span class=\"math-tex\">$u_n$<\/span>&nbsp;l&agrave;<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$u_n=-5+4n$<\/span>","B. <span class=\"math-tex\">$u_n=-1-4n$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$u_n=-5+4n^2$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$u_n=-9+4n$<\/span>"],"correct":"4","level":"1","hint":"","answer":"<p>C&ocirc;ng th\u1ee9c t\u1ed5ng qu&aacute;t c\u1ee7a c\u1ea5p s\u1ed1 c\u1ed9ng l&agrave;&nbsp;<span class=\"math-tex\">$u_n=u_1+(n-1)d$<\/span>&nbsp;.<\/p><p>V\u1edbi&nbsp;<span class=\"math-tex\">$u_1=-5,d=4$<\/span>, khi \u0111&oacute;&nbsp;<span class=\"math-tex\">$u_n=-5+(n-1).4$<\/span>&nbsp;hay&nbsp;<span class=\"math-tex\">$u_n=-9+4n$<\/span>&nbsp;.<\/p><p>Ch\u1ecdn&nbsp; &nbsp;<span style=\"color:#16a085;\"><strong>D.<\/strong>&nbsp;<span class=\"math-tex\">$u_n=-9+4n$<\/span>.<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-13 01:28:34","option_type":"math","len":0}]}