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+3x20-x^2+3x-2 \geq 0 is ______.

A number or a short expression. Spacing, $ signs and \frac vs / are all fine.

Official solution

Given the inequality x2+3x20-x^2 + 3x - 2 \geq 0,
we can rewrite it as x23x+20x^2 - 3x + 2 \leq 0.
This can be factored into (x2)(x1)0(x - 2)(x - 1) \leq 0.

To analyze the inequality (x2)(x1)0(x - 2)(x - 1) \leq 0, we find the roots of the corresponding equation (x2)(x1)=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 (x2)(x - 2) and (x1)(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 1x21 \leq x \leq 2.

Therefore, the solution set is {x1x2}\boxed{\{x | 1 \leq x \leq 2\}}.

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic, difficulty and ordering added by this site.