1958 AMC 12 第 34 题

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34.

一个分数的分子为 6x+16x+1,分母为 74x7-4x,且 xx 可取从 2-222 的任意值,包括两端。使分子大于分母的 xx 值为:

The numerator of a fraction is 6x+1,6x+1, the denominator is 74x,7-4x, and xx can have any value between 2-2 and 2,2, both included. The values of xx for which the numerator is greater than the denominator are:

35<x2\dfrac35\lt x\le2

35x2\dfrac35\le x\le2

0<x20\lt x\le2

0x20\le x\le2

2x2-2\le x\le2

答案:A
知识点:不等式一次方程
难度评级:1110
小提示:

直接解不等式 6x+1>74x6x+1\gt7-4x 来比较分子与分母

Compare the numerator and denominator directly by solving 6x+1>74x6x+1\gt7-4x

大提示:

将所得不等式的解集与给定区间 [2,2][-2,2] 取交集

Intersect the resulting inequality with the given interval [2,2][-2,2]

解答:

所需比较给出 6x+1>74x 6x+1\gt7-4x\text{,}所以 10x>610x\gt6,且 x>35x\gt\frac{3}{5}。与 2x2-2\le x\le2 取交集得到 35<x2 \frac35\lt x\le2\text{。}

所以正确答案为 A

The required comparison gives 6x+1>74x, 6x+1\gt7-4x, so 10x>610x\gt6 and x>35.x\gt\frac{3}{5}. Intersecting this with 2x2-2\le x\le2 gives 35<x2. \frac35\lt x\le2.

Thus, the correct answer is A.

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