视频 BV15i4y1N7Nd 题12. 选项判定
A.
729＜1728
即3^6＜12^3
即log(3)(3^6)＜log(3)(12^3)
即6·log(3)(3)＜3·log(3)(12)
即6·1＜3·log(3)(12)
即6z＜3x
ln3/3＞ln4/4
即4ln3＞3ln4
即ln3^4＞ln4^3
即3^4＞4^3
即3^(1/3)＞4^(1/4)
即log(12)(3^(1/3))＞log(12)(4^(1/4))
即1/3log(12)(3)＞1/4log(12)(4)
即1/(3·log(3)(12))＞1/(4·log(4)(12))
即3·log(3)(12)＜4·log(4)(12)
即3x＜4y
综述
6z＜3x＜4y
C.
log(3)(4)，log(4)(3)＞0
且log(3)(4)≠log(4)(3)
即2+log(3)(4)+log(4)(3)＞4
即1+log(3)(4)+1+log(4)(3)＞4
即log(3)(12)+log(4)(12)＞4·1
即x+y＞4z
ps.
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