1962 AMC 12 第 29 题

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29.

下列哪组 xx 值满足不等式 2x2+x<62x^2+x\lt6

Which of the following sets of xx-values satisfy the inequality 2x2+x<6?2x^2+x\lt6?

2<x<32-2\lt x\lt\dfrac32

x>32x\gt\dfrac32x<2x\lt-2

x>32x\gt\dfrac32 or x<2x\lt-2

x<32x\lt\dfrac32

32<x<2\dfrac32\lt x\lt2

x<2x\lt-2

答案:A
知识点:不等式因式分解零积性质
难度评级:1150
小提示:

将所有项移到一边,并分解二次式

Move all terms to one side and factor the quadratic

大提示:

两个一次因式的乘积在两根之间为负

A product of two linear factors is negative between its roots

解答:

该不等式为 2x2+x6<02x^2+x-6\lt0。分解得 (2x3)(x+2)<0(2x-3)(x+2)\lt0。乘积在两根之间为负,所以 2<x<32-2\lt x\lt\frac{3}{2}

所以正确答案是 A

The inequality is 2x2+x6<0.2x^2+x-6\lt0. Factoring gives (2x3)(x+2)<0.(2x-3)(x+2)\lt0. The product is negative between its roots, so 2<x<32.-2\lt x\lt\frac{3}{2}.

Thus, the correct answer is A.

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