{"common":{"save":0,"post_id":"7934","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"8324","post_id":"7934","mon_id":"1159278","chapter_id":"1159329","question":"<p>Di\u1ec7n tích c\u1ee7a hình vành khuyên n\u1eb1m gi\u1eefa hai \u0111\u01b0\u1eddng tròn \u0111\u1ed3ng tâm có bán kính là 3 m và 4 m là:<\/p>","options":["<strong>A.<\/strong> <span class=\"math-tex\">$8\\pi$<\/span> m²","<strong>B.<\/strong> <span class=\"math-tex\">$6\\pi$<\/span> m²","<strong>C.<\/strong> <span class=\"math-tex\">$4\\pi$<\/span> m²","<strong>D.<\/strong> <span class=\"math-tex\">$7\\pi$<\/span> m²"],"correct":"4","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>D.<\/strong> <span class=\"math-tex\">$7\\pi$<\/span> m².<\/span><\/p><p>Di\u1ec7n tích c\u1ee7a hình vành khuyên n\u1eb1m gi\u1eefa hai \u0111\u01b0\u1eddng tròn \u0111\u1ed3ng tâm có bán kính là 3 m và<br \/>4 m là: <span class=\"math-tex\">$S=\\pi(R^2-r^2)=\\pi(4^2-3^2)=7\\pi$<\/span> m².<\/p><p>(v\u1edbi R > r).<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2024-11-04 01:59:52","option_type":"math","len":0},{"id":"8326","post_id":"7934","mon_id":"1159278","chapter_id":"1159329","question":"<p>S\u1ed1 \u0111o cung có \u0111\u1ed9 dài 10<span class=\"math-tex\">$\\pi$<\/span> c\u1ee7a \u0111\u01b0\u1eddng tròn bán kính 25 cm là:<\/p>","options":["<strong>A.<\/strong> 42°","<strong>B.<\/strong> 72°","<strong>C.<\/strong> 36°","<strong>D.<\/strong> 54°"],"correct":"2","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>B.<\/strong> 72°.<\/span><\/p><p>S\u1ed1 \u0111o cung có \u0111\u1ed9 dài 10<span class=\"math-tex\">$\\pi$<\/span> c\u1ee7a \u0111\u01b0\u1eddng tròn bán kính 25 cm là:<\/p><p><span class=\"math-tex\">$l=\\dfrac{\\pi.R.n}{180}$<\/span> ⇒ <span class=\"math-tex\">$n=\\dfrac{l.180}{\\pi.R}$<\/span> hay <span class=\"math-tex\">$n=\\dfrac{10\\pi.180}{\\pi.25}=$<\/span> 72°.<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2024-11-04 02:05:23","option_type":"txt","len":0},{"id":"8328","post_id":"7934","mon_id":"1159278","chapter_id":"1159329","question":"<p>Cho \u0111\u01b0\u1eddng tròn (O ; R), \u0111\u1ed9 dài <span class=\"math-tex\">$\\stackrel\\frown{AB}$<\/span> là <span class=\"math-tex\">$\\dfrac{\\pi R}{4}$<\/span>, s\u0111 <span class=\"math-tex\">$\\stackrel\\frown{AB}$<\/span> là:<\/p>","options":["<strong>A.<\/strong> 45°","<strong>B.<\/strong> 60°","<strong>C.<\/strong> 135°","<strong>D.<\/strong> 90°"],"correct":"1","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>A.<\/strong> 45°.<\/span><\/p><p>G\u1ecdi n° là s\u1ed1 \u0111o cung nh\u1ecf AB.<\/p><p>Ta có <span class=\"math-tex\">$l=\\dfrac{\\pi.R.n}{180}$<\/span> ⇒ <span class=\"math-tex\">$n=\\dfrac{l.180}{\\pi.R}$<\/span> hay <span class=\"math-tex\">$n=\\dfrac{\\dfrac{\\pi.R}{4}.180}{\\pi.R}=45^0$<\/span>.<\/p><p>V\u1eady s\u0111 <span class=\"math-tex\">$\\stackrel\\frown{AB}$<\/span> = 45°.<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2024-11-04 02:13:47","option_type":"txt","len":1}]}
