{"common":{"save":0,"post_id":"7868","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"8003","post_id":"7868","mon_id":"1159278","chapter_id":"1159328","question":"<p>Cho ΔABC có AB = 12 cm, AC = 16 cm, BC = 20 cm. Làm tròn \u0111\u1ebfn \u0111\u1ed9, s\u1ed1 \u0111o góc B là:<\/p>","options":["<strong>A.<\/strong> 45°","<strong>B.<\/strong> 58°","<strong>C.<\/strong> 53°","<strong>D.<\/strong> 42°"],"correct":"3","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>C.<\/strong> 53°<\/span><\/p><p>Ta có: <span class=\"math-tex\">$AB^2+AC^2=12^2+16^2=400=20^2=BC^2$<\/span> suy ra <span class=\"math-tex\">$AB^2+AC^2=BC^2$<\/span><\/p><p>Do \u0111ó ΔABC vuông \u1edf A (\u0111\u1ecbnh lí Pythagore \u0111\u1ea3o).<\/p><p><span class=\"math-tex\">$\\sin B=\\dfrac{AC}{BC}=\\dfrac{16}{20}=0,8$<\/span> suy ra <span class=\"math-tex\">$\\widehat{B}\\approx 53^o$<\/span>.<\/p>","type":"choose","extra_type":"shape1","time":"0","user_id":"127","test":"0","date":"2024-10-21 02:15:18","option_type":"txt","len":0},{"id":"8007","post_id":"7868","mon_id":"1159278","chapter_id":"1159328","question":"<p>Vi\u1ebft t\u1ec9 s\u1ed1 l\u01b0\u1ee3ng giác góc cos 61° thành t\u1ec9 s\u1ed1 l\u01b0\u1ee3ng giác c\u1ee7a góc nh\u1ecf h\u01a1n 45° ta \u0111\u01b0\u1ee3c:<\/p>","options":["<strong>A.<\/strong> cot 29°","<strong>B.<\/strong> sin 29°","<strong>C.<\/strong> –sin 29°","<strong>D.<\/strong> tan 29°"],"correct":"2","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#27ae60;\"><\/span><span style=\"color:#16a085;\"><strong>B.<\/strong> sin 29°<\/span><\/p><p>N\u1ebfu hai góc ph\u1ee5 nhau thì sin góc này b\u1eb1ng cos góc kia nên <span style=\"color:#16a085;\"><strong>cos 61° = sin (90° – 61°) = sin 29°<\/strong><\/span>.<\/p>","type":"choose","extra_type":"classic","time":"0","user_id":"127","test":"0","date":"2024-10-21 02:27:29","option_type":"txt","len":2},{"id":"8008","post_id":"7868","mon_id":"1159278","chapter_id":"1159328","question":"<p>Vi\u1ebft t\u1ec9 s\u1ed1 l\u01b0\u1ee3ng giác góc cot 36° thành t\u1ec9 s\u1ed1 l\u01b0\u1ee3ng giác c\u1ee7a góc l\u1edbn h\u01a1n 45° ta \u0111\u01b0\u1ee3c:<\/p>","options":["<strong>A.<\/strong> tan 54°","<strong>B.<\/strong> sin 54°","<strong>C.<\/strong> cos 54°","<strong>D.<\/strong> –tan 54°"],"correct":"1","level":"2","hint":"","answer":"<p>Ch\u1ecdn <span style=\"color:#16a085;\"><strong>A.<\/strong> tan 54°<\/span><\/p><p>N\u1ebfu hai góc ph\u1ee5 nhau thì tan góc này b\u1eb1ng cot góc kia nên: <span class=\"math-tex\">$\\cot36^0=\\tan(90^0-36^0)=\\tan54^0$<\/span>.<\/p>","type":"choose","extra_type":"shape1","time":"0","user_id":"127","test":"0","date":"2024-10-21 02:29:24","option_type":"txt","len":0}]}
