Over all reals

Algebra Level 3

2016 ( a 3 b + b 3 c + c 3 a ) 2016(a^3b + b^3c + c^3a)

Over all triples of real numbers ( a , b , c ) (a,b,c) which satisfy a + b + c = 0 a+b+c = 0 , find the maximum value of the expression above.


The answer is 0.

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1 solution

Manuel Kahayon
May 11, 2017

Notice that

( a 2 + a b + b 2 ) 2 + ( a 3 b + b 3 c + c 3 a ) = ( a + b + c ) ( a 3 + 2 a 2 b + a b 2 + b 3 a 2 c a b c + a c 2 ) = 0 (a^2 + ab + b^2)^2 + (a^3b + b^3c + c^3a) = (a+b+c)(a^3 + 2 a^2 b + a b^2 + b^3 - a^2 c - a b c + a c^2) = 0

Implying that 2016 ( a 3 b + b 3 c + c 3 a ) = 2016 ( a 2 + a b + b 2 ) 2 0 2016(a^3b + b^3c + c^3a) = -2016(a^2 + ab + b^2)^2 \leq 0 ,

With equality if a = b = c = 0 a = b = c = 0 .

Thus, the maximum is 0 \boxed{0} .

Wow a, manonotice pala namin yan, haha

Pil Pinas - 4 years, 1 month ago

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Nanotice mo nga eh

Manuel Kahayon - 4 years, 1 month ago

aha I found you

EN C - 4 years ago

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