{"common":{"save":0,"post_id":"7994","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"11736","post_id":"7994","mon_id":"1159278","chapter_id":"1159334","question":"<p>Hình c\u1ea7u có th\u1ec3 tích là <span class=\"math-tex\">$288\\pi$<\/span> (cm³) thì di\u1ec7n tích m\u1eb7t c\u1ea7u \u0111ó là<\/p>","options":["<strong>A.<\/strong> 144 cm².","<strong>B.<\/strong> <span class=\"math-tex\">$144\\pi$<\/span> cm².","<strong>C.<\/strong> <span class=\"math-tex\">$72\\pi$<\/span> cm².","<strong>D.<\/strong> 72 cm²."],"correct":"2","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>B.<\/strong> <span class=\"math-tex\">$144\\pi$<\/span> cm².<\/span><\/p><p>Hình c\u1ea7u tâm O bán kính R có th\u1ec3 tích là <span class=\"math-tex\">$V=\\dfrac{4\\pi R^3}{3}$<\/span>.<\/p><p>Suy ra <span class=\"math-tex\">$R^3=\\dfrac{3V}{4\\pi}$<\/span> hay <span class=\"math-tex\">$R=\\sqrt[3]{\\dfrac{3V}{4\\pi}}=\\sqrt[3]{\\dfrac{3.288\\pi}{4\\pi}}=6$<\/span> (cm).<\/p><p>Di\u1ec7n tích c\u1ee7a m\u1eb7t c\u1ea7u \u0111ó là <span class=\"math-tex\">$S=4\\pi R^2=4\\pi.6^2=144\\pi$<\/span> (cm²).<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2025-05-30 08:16:34","option_type":"math","len":0},{"id":"11737","post_id":"7994","mon_id":"1159278","chapter_id":"1159334","question":"<p>\u0110\u01b0\u1eddng kính c\u1ee7a qu\u1ea3 bóng tennis là 2,63 inch. H\u1ecfi b\u1ec1 m\u1eb7t c\u1ee7a nó có di\u1ec7n tích bao nhiêu centimet vuông (k\u1ebft qu\u1ea3 làm tròn \u0111\u1ebfn ch\u1eef s\u1ed1 th\u1eadp phân th\u1ee9 nh\u1ea5t)? (l\u1ea5y π = 3,14 và 1 inch = 2,54 cm)<\/p>","options":["<strong>A.<\/strong> 560,4 cm².","<strong>B.<\/strong> 84,4 cm².","<strong>C.<\/strong> 560,5 cm².","<strong>D.<\/strong> 140,1 cm²."],"correct":"4","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>D.<\/strong> 140,1 cm².<\/span><\/p><p>Bán kính c\u1ee7a qu\u1ea3 bòng tennis là R = 2,63 : 2 = 1,315 inch = 3,3401 (cm).<\/p><p>Di\u1ec7n tích b\u1ec1 m\u1eb7t c\u1ee7a qu\u1ea3 bóng là S = 4 . 3,14 . 3,3401² ≈ 140,1 (cm²).<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2025-05-30 08:22:16","option_type":"txt","len":2},{"id":"11738","post_id":"7994","mon_id":"1159278","chapter_id":"1159334","question":"<p>Qu\u1ea3 bóng khúc côn c\u1ea7u có d\u1ea1ng hình c\u1ea7u có \u0111\u1ed9 dài \u0111\u01b0\u1eddng tròn l\u1edbn là 23cm. Tính th\u1ec3 tích c\u1ee7a qu\u1ea3 bóng (làm tròn k\u1ebft qu\u1ea3 \u0111\u1ebfn ch\u1eef s\u1ed1 th\u1eadp phân th\u1ee9 2, l\u1ea5y π ≈ 3,14).<\/p>","options":["<strong>A.<\/strong> 205,67 cm³.","<strong>B.<\/strong> 2027,81 cm³.","<strong>C.<\/strong> 2027,84 cm³.","<strong>D.<\/strong> 50 939,17 cm³."],"correct":"1","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>A.<\/strong> 205,67 cm³.<\/span><\/p><p>G\u1ecdi R (R > 0, \u0111\u01a1n v\u1ecb cm) là bán kính c\u1ee7a qu\u1ea3 bóng khúc khôn c\u1ea7u.<\/p><p>Vì \u0111\u1ed9 dài \u0111\u01b0\u1eddng tròn l\u1edbn là 23 cm nên <span class=\"math-tex\">$2\\pi R$<\/span> = 23.<\/p><p>Suy ra R = <span class=\"math-tex\">$\\dfrac{23}{2\\pi}\\approx\\dfrac{23}{2.3,14}=\\dfrac{575}{157}$<\/span> (cm).<\/p><p>Th\u1ec3 tích c\u1ee7a qu\u1ea3 bóng là <span class=\"math-tex\">$V=\\dfrac{4}{3}.\\pi.R^3\\approx\\dfrac{4}{3}.3,14.\\bigg(\\dfrac{575}{157}\\bigg)^3$<\/span> ≈ 205,67 (cm³).<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2025-05-30 08:33:49","option_type":"txt","len":2}]}