{"common":{"save":0,"post_id":"6321","level":2,"total":10,"point":10,"point_extra":0},"segment":[{"id":"5826","mon_id":"1158767","chapter_id":"1158829","post_id":"6321","question":"<p>Cho bi\u1ebft <span class=\"math-tex\">$\\cos \\alpha=-\\frac{2}{3}$<\/span>&nbsp;. T&iacute;nh <span class=\"math-tex\">$\\tan \\alpha$<\/span>&nbsp;?<\/p>","options":["A.<span class=\"math-tex\">$\\frac{5}{4}$<\/span> .","B. <span class=\"math-tex\">$-\\frac{5}{2}$<\/span> .","C. <span class=\"math-tex\">$\\frac{\\sqrt{5}}{2}$<\/span> .","D. <span class=\"math-tex\">$-\\frac{\\sqrt{5}}{2}$<\/span> ."],"correct":"4","level":"2","hint":"","answer":"<p><span style=\"color:#27ae60;\"><strong>Ch\u1ecdn&nbsp;&nbsp; &nbsp;D.<br \/>Do <span class=\"math-tex\">$\\cos \\alpha<0\\Rightarrow\\tan\\alpha<0$<\/span>&nbsp;.<br \/>Ta c&oacute;: &nbsp; <span class=\"math-tex\">$1+\\tan^2\\alpha=\\frac{1}{\\cos^2 \\alpha}\\Leftrightarrow \\tan^2\\alpha=\\frac{5}{4}\\Rightarrow \\tan\\alpha=-\\frac{\\sqrt{5}}{2}$<\/span>&nbsp;.<\/strong><\/span><\/p>","type":"choose","extra_type":"classic","user_id":"147","test":"0","date":"2022-10-19 02:22:20","option_type":"math","len":0},{"id":"5827","mon_id":"1158767","chapter_id":"1158829","post_id":"6321","question":"<p>Cho bi\u1ebft <span class=\"math-tex\">$\\tan\\alpha=\\frac{1}{2}$<\/span>&nbsp;. T&iacute;nh <span class=\"math-tex\">$\\cot \\alpha$<\/span>&nbsp;.<\/p>","options":["A.<span class=\"math-tex\">$\\cot\\alpha=2$<\/span> . ","B. <span class=\"math-tex\">$\\cot\\alpha=\\sqrt{2}$<\/span> .","C. <span class=\"math-tex\">$\\cot\\alpha=\\frac{1}{4}$<\/span> . ","D. <span class=\"math-tex\">$\\cot\\alpha=\\frac{1}{2}$<\/span> ."],"correct":"1","level":"2","hint":"","answer":"<p><span style=\"color:#27ae60;\"><strong>Ch\u1ecdn&nbsp;&nbsp; &nbsp;A.<br \/>&nbsp;<span class=\"math-tex\">$\\tan\\alpha.\\cot \\alpha=1\\Rightarrow\\frac{1}{\\tan \\alpha}=2$<\/span>.<\/strong><\/span><\/p>","type":"choose","extra_type":"classic","user_id":"147","test":"0","date":"2022-10-19 02:26:41","option_type":"math","len":0},{"id":"5828","mon_id":"1158767","chapter_id":"1158829","post_id":"6321","question":"<p><span class=\"math-tex\">$\\cos\\alpha$<\/span>&nbsp; b\u1eb1ng bao nhi&ecirc;u n\u1ebfu <span class=\"math-tex\">$\\cot \\alpha=-\\frac{1}{2}$<\/span>&nbsp;?<\/p>","options":["A. <span class=\"math-tex\">$\\pm\\frac{\\sqrt{5}}{5}$<\/span> .","B. <span class=\"math-tex\">$\\frac{\\sqrt{5}}{2}$<\/span> . "," C. <span class=\"math-tex\">$-\\frac{\\sqrt{5}}{5}$<\/span> .","D. <span class=\"math-tex\">$-\\frac{1}{3}$<\/span> ."],"correct":"1","level":"2","hint":"","answer":"<p><span style=\"color:#27ae60;\"><strong>Ch\u1ecdn A<br \/>Ta c&oacute; <span class=\"math-tex\">$\\cot \\alpha=-\\frac{1}{2}\\Rightarrow\\tan\\alpha=-2$<\/span>&nbsp;.<br \/>&nbsp;<span class=\"math-tex\">$1+\\tan^2\\alpha=\\frac{1}{\\cos^2 \\alpha}\\Leftrightarrow\\cos^2 \\alpha=\\frac{1}{1+\\tan^2 \\alpha}=\\frac{1}{1+(-2)^2}=\\frac{1}{5}$<\/span>.<br \/>Suy ra <span class=\"math-tex\">$\\cos \\alpha=\\pm\\frac{\\sqrt{5}}{5}$<\/span>&nbsp;.<\/strong><\/span><\/p>","type":"choose","extra_type":"classic","user_id":"147","test":"0","date":"2022-10-19 02:34:22","option_type":"math","len":0}]}