Dizzy algebra Part - II

Algebra Level 3

If a + b + c = 0 a+b+c=0 then find the value of

a 4 + b 4 + c 4 a 2 b 2 + b 2 c 2 + c 2 a 2 \frac { { a }^{ 4 }+{ b }^{ 4 }+{ c }^{ 4 } }{ { a }^{ 2 }{ b }^{ 2 }+{ b }^{ 2 }{ c }^{ 2 }+{ c }^{ 2 }{ a }^{ 2 } }


The answer is 2.

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1 solution

Tunk-Fey Ariawan
Mar 17, 2014

Let a 4 + b 4 + c 4 a 2 b 2 + b 2 c 2 + a 2 c 2 = k , \frac{a^4+b^4+c^4}{a^2b^2+b^2c^2+a^2c^2}=k, then a 4 + b 4 + c 4 = k ( a 2 b 2 + b 2 c 2 + a 2 c 2 ) a 4 + b 4 + c 4 k ( a 2 b 2 + b 2 c 2 + a 2 c 2 ) = 0. ( 1 ) \begin{aligned} a^4+b^4+c^4&=k(a^2b^2+b^2c^2+a^2c^2)\\ a^4+b^4+c^4-k(a^2b^2+b^2c^2+a^2c^2)&=0.&\;(1) \end{aligned} By using Heron's formula , we obtain a 4 + b 4 + c 4 2 ( a 2 b 2 + b 2 c 2 + a 2 c 2 ) = ( a + b + c ) ( a b c ) ( a b + c ) ( a + b c ) . a^4+b^4+c^4-2(a^2b^2+b^2c^2+a^2c^2)=(a+b+c)(a-b-c)(a-b+c)(a+b-c). Since a + b + c = 0 a+b+c=0 , we have a 4 + b 4 + c 4 2 ( a 2 b 2 + b 2 c 2 + a 2 c 2 ) = 0. ( 2 ) \begin{aligned} a^4+b^4+c^4-2(a^2b^2+b^2c^2+a^2c^2)&=0.&&&&&&&&&&\;(2) \end{aligned} Comparing ( 1 ) (1) and ( 2 ) (2) yields k = 2 k=\boxed{2} .

I just substituted a as -1 , b as 1 , c as 0

solver pro - 7 years, 2 months ago

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Yeah, me too.

Finn Hulse - 7 years, 2 months ago

yeah it.s hit and trial , me too

Mohit Gupta - 7 years, 2 months ago

Great explanation!!!

milind prabhu - 7 years, 2 months ago

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