{"common":{"save":0,"post_id":"7051","level":1,"total":10,"point":10,"point_extra":0},"segment":[{"id":"4854","post_id":"7051","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho dãy s\u1ed1 <span class=\"math-tex\">$(u_n)$<\/span> \u0111\u01b0\u1ee3c xác \u0111\u1ecbnh b\u1edfi <span class=\"math-tex\">$u_1=\\dfrac{1}{3}$<\/span> và <span class=\"math-tex\">$u_n=3u_{n-1}$<\/span> , <span class=\"math-tex\">$\\forall n\\ge 2$<\/span> . S\u1ed1 h\u1ea1ng th\u1ee9 n\u0103m c\u1ee7a dãy s\u1ed1 <span class=\"math-tex\">$(u_n)$<\/span> là<\/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><span class=\"math-tex\">$u_n=3u_{n-1}$<\/span> , <span class=\"math-tex\">$\\forall n\\ge 2$<\/span> ⇒ <span class=\"math-tex\">$q=3$<\/span> ⇒ <span class=\"math-tex\">$u_n=u_1.q^{n-1}=\\dfrac{1}{3}.3^{n-1}=3^{n-2}$<\/span> .<\/p><p>⇒ <span class=\"math-tex\">$u_5=3^3 = 27$<\/span><\/p><p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>A.<\/strong> 27.<\/span><\/p>","type":"choose","extra_type":"shape1","user_id":"131","test":"0","date":"2023-12-06 01:43:42","option_type":"txt","len":0},{"id":"4855","post_id":"7051","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho c\u1ea5p s\u1ed1 nhân <span class=\"math-tex\">$(u_n)$<\/span> có s\u1ed1 h\u1ea1ng \u0111\u1ea7u <span class=\"math-tex\">$u_1=-2$<\/span> và <span class=\"math-tex\">$u_6=486$<\/span>. Công b\u1ed9i <span class=\"math-tex\">$q$<\/span> b\u1eb1ng<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$q=3$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$q=-3$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$q=\\dfrac{1}{3}$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$q=-\\dfrac{1}{3}$<\/span>"],"correct":"2","level":"1","hint":"","answer":"<p>Theo \u0111\u1ec1 ta có<\/p><p><span class=\"math-tex\">$\\begin{cases}u_1=-2\\\\u_6=486\\end{cases}$<\/span> ⇔ <span class=\"math-tex\">$\\begin{cases}u_1=-2\\\\-2.q^5=486\\end{cases}$<\/span> ⇒ <span class=\"math-tex\">$q^5=-243$<\/span> ⇒ <span class=\"math-tex\">$q=-3$<\/span><\/p><p>Ch\u1ecdn <span style=\"color:#16a085;\"> <strong>B.<\/strong> <span class=\"math-tex\">$q=-3$<\/span> .<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-06 01:48:41","option_type":"math","len":0},{"id":"4857","post_id":"7051","mon_id":"1158924","chapter_id":"1159147","question":"<p>Cho c\u1ea5p s\u1ed1 nhân 128 ; 64 ; 32 ; 16 ; 8 , công b\u1ed9i c\u1ee7a c\u1ea5p s\u1ed1 nhân \u0111ó là<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$q=\\dfrac{1}{2}$<\/span>","<strong>B.<\/strong> <span class=\"math-tex\">$q=2$<\/span>","<strong>C.<\/strong> <span class=\"math-tex\">$q=\\sqrt{2}$<\/span>","<strong>D.<\/strong> <span class=\"math-tex\">$q=\\dfrac{1}{\\sqrt{2}}$<\/span>"],"correct":"1","level":"1","hint":"","answer":"<p><span class=\"math-tex\">$u_1=128$<\/span> ; <span class=\"math-tex\">$u_2=64$<\/span><\/p><p>Vì <span class=\"math-tex\">$u_2=q.u_1$<\/span> nên <span class=\"math-tex\">$64 = q.128$<\/span> ⇒ <span class=\"math-tex\">$q=\\dfrac{1}{2}$<\/span> .<\/p><p>Ch\u1ecdn <span style=\"color:#16a085;\"> <strong>A.<\/strong> <span class=\"math-tex\">$q=\\dfrac{1}{2}$<\/span> .<\/span><\/p>","type":"choose","extra_type":"classic","user_id":"131","test":"0","date":"2023-12-06 01:52:06","option_type":"math","len":0}]}
