Maths Olympiad Prep

Track / Stage 3 / 153 of 260 #153 of 1964

Problem 153

AMC 10/12, early questions
Algebra Difficulty 3.4 Find the answer

The solution set for the inequality −x2+3x−2≥0-x^2+3x-2 \geq 0 is ______.

A number or a short expression. Fractions can be typed as 3/2, and spacing doesn't matter.

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Official solution

Given the inequality −x2+3x−2≥0-x^2 + 3x - 2 \geq 0,
we can rewrite it as x2−3x+2≤0x^2 - 3x + 2 \leq 0.
This can be factored into (x−2)(x−1)≤0(x - 2)(x - 1) \leq 0.

To analyze the inequality (x−2)(x−1)≤0(x - 2)(x - 1) \leq 0, we find the roots of the corresponding equation (x−2)(x−1)=0(x - 2)(x - 1) = 0, which are x=2x = 2 and x=1x = 1. Since the inequality is less than or equal to zero, we are interested in the interval where the product of the two factors does not exceed zero.

- For x2x 2, both factors (x−2)(x - 2) and (x−1)(x - 1) are positive, which makes their product positive.

Based on this analysis, the solution set for the inequality is the interval where the product is non-positive, which occurs when 1≤x≤21 \leq x \leq 2.

Therefore, the solution set is {x∣1≤x≤2}\boxed{\{x | 1 \leq x \leq 2\}}.

Source: NuminaMath-1.5, licensed Apache-2.0. Statement reproduced verbatim; metadata (topic, difficulty, ordering) added by this project.