MATHS OLYMPIAD [stage1] 2018 (INDIA)

Algebra Level 3

Integers a a , b b , and c c satisfy

{ a + b c = 1 a 2 + b 2 c 2 = 1 \large \begin{cases} a + b - c = 1 \\ a^2+ b^2 - c^2 = -1\end{cases}

What is the sum of all possible values of a 2 + b 2 + c 2 a^2+ b^2 + c^2 ?


The answer is 18.

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1 solution

Anshaj Shukla
Aug 19, 2018

a + b – c = 1, a^2 + b^2– c^2 = – 1 a + b – 1= c

a^2 + b^2 + 1 + 2ab – 2(a + b) = c^2

  • ab = a + b

 (a – 1) (b – 1) = 1

So a – 1 = b – 1 = ±1

a = b = 2 or a = b = 0

So c = 3 (when a = b = 2) or c = –1 (when a = b = 0)

Hence a^2 + b^2 + c^2 = 17 or 1

Sum = 18

This came in PRMO 2018!!!

Mr. India - 2 years, 4 months ago

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yes u correct

Anshaj Shukla - 2 years ago

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