Cho a > 1. Mệnh đề nào sau đây là đúng?

Giải thích

Chọn C. Xét đáp án A có a 3 a 2 ​ ​ = a 3 − 1 ​ = 3 a ​ 1 ​ < 1 , ∀ a > 1 nên loại. Xét đáp án B có a ​ = a 2 1 ​ > a 3 1 ​ , ∀ a > 1 nên loại. Xét đáp án C có mà 1" data-mathml="«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«mn»0«/mn»«mo»§#60;«/mo»«msup»«mi»a«/mi»«msqrt»«mn»3«/mn»«/msqrt»«/msup»«mo»§#60;«/mo»«msup»«mi»a«/mi»«msqrt»«mn»5«/mn»«/msqrt»«/msup»«mo»,«/mo»«mo»§#8704;«/mo»«mi»a«/mi»«mo»§#62;«/mo»«mn»1«/mn»«/math»" role="math" src="data:image/png;base64,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" style="max-width: none;">do \frac1{a^\sqrt5}" data-mathml="«math xmlns=¨http://www.w3.org/1998/Math/MathML¨»«msqrt»«mn»3«/mn»«/msqrt»«mo»§#60;«/mo»«msqrt»«mn»5«/mn»«/msqrt»«mo»§#8658;«/mo»«mfrac»«mn»1«/mn»«msup»«mi»a«/mi»«msqrt»«mn»3«/mn»«/msqrt»«/msup»«/mfrac»«mo»§#62;«/mo»«mfrac»«mn»1«/mn»«msup»«mi»a«/mi»«msqrt»«mn»5«/mn»«/msqrt»«/msup»«/mfrac»«/math»" role="math" src="data:image/png;base64,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" style="max-width: none;"> Nên chọn C. Xét đáp án D có a 2016 < a 2017 , ∀ a > 1 ⇒ a 2016 1 ​ > a 2017 1 ​ nên loại.