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OlympiadBench / 1807 / Let q be a real number. Gugu has a napkin with ten distinct real numbers…

Problem

Answer published by the source. Consult the official source to check your work against its answer.

answer type

Numerical

is multiple answer

true

language

English

question

Let qq be a real number. Gugu has a napkin with ten distinct real numbers written on it, and he writes the following three lines of real numbers on the blackboard: - In the first line, Gugu writes down every number of the form aba-b, where aa and bb are two (not necessarily distinct) numbers on his napkin. - In the second line, Gugu writes down every number of the form qabq a b, where aa and bb are two (not necessarily distinct) numbers from the first line. - In the third line, Gugu writes down every number of the form a2+b2c2d2a^{2}+b^{2}-c^{2}-d^{2}, where a,b,c,da, b, c, d are four (not necessarily distinct) numbers from the first line. Determine all values of qq such that, regardless of the numbers on Gugu's napkin, every number in the second line is also a number in the third line.
Plain-text mathematical notation (without MathML)
Let q be a real number. Gugu has a napkin with ten distinct real numbers written on it, and he writes the following three lines of real numbers on the blackboard:

- In the first line, Gugu writes down every number of the form a−b, where a and b are two (not necessarily distinct) numbers on his napkin.
- In the second line, Gugu writes down every number of the form qab, where a and b are two (not necessarily distinct) numbers from the first line.
- In the third line, Gugu writes down every number of the form a²+b²−c²−d², where a,b,c,d are four (not necessarily distinct) numbers from the first line.

Determine all values of q such that, regardless of the numbers on Gugu's napkin, every number in the second line is also a number in the third line.
Original LaTeX notation
Let $q$ be a real number. Gugu has a napkin with ten distinct real numbers written on it, and he writes the following three lines of real numbers on the blackboard:

- In the first line, Gugu writes down every number of the form $a-b$, where $a$ and $b$ are two (not necessarily distinct) numbers on his napkin.
- In the second line, Gugu writes down every number of the form $q a b$, where $a$ and $b$ are two (not necessarily distinct) numbers from the first line.
- In the third line, Gugu writes down every number of the form $a^{2}+b^{2}-c^{2}-d^{2}$, where $a, b, c, d$ are four (not necessarily distinct) numbers from the first line.

Determine all values of $q$ such that, regardless of the numbers on Gugu's napkin, every number in the second line is also a number in the third line.

question type

Open-ended

subject

Math

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