Maths Olympiad Prep

Library / /8 of 377

Algebra Difficulty 4.1 AIME Find the answer United States

Problem:

How many real numbers xx are solutions to the following equation?
x1=x2+x3 |x-1|=|x-2|+|x-3|

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

Solution

Solution:

If x<1x<1, the equation becomes (1x)=(2x)+(3x)(1-x)=(2-x)+(3-x) which simplifies to x=4x=4, contradicting the assumption x<1x<1.

If 1x21 \leq x \leq 2, we get (x1)=(2x)+(3x)(x-1)=(2-x)+(3-x), which gives x=2x=2.

If 2x32 \leq x \leq 3, we get (x1)=(x2)+(3x)(x-1)=(x-2)+(3-x), which again gives x=2x=2.

If x3x \geq 3, we get (x1)=(x2)+(x3)(x-1)=(x-2)+(x-3), or x=4x=4.

So 22 and 44 are the only solutions, and the answer is 22.

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.