Interesting answer

Algebra Level 3

If the equation 1 + ( x 1 ) x 2 1 1 x 3 + 1 = 1 \large \frac{\frac{1+(x-1)}{x^2-1}}{\frac{1}{x^3+1}}=1 has the same solutions as the equation x 3 + b x 2 + c x + d x^3+bx^2+cx+d . Find b + c + d b+c+d .


The answer is 0.

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1 solution

Ruslan Abdulgani
Feb 4, 2015

The equation can be simplified as [x/((x+1)(x-1))] (x+1)(x2 – x +1) = 1. So x3 – x2 + x = x – 1, or x3 – x2 + 1 = 0. b=-1, c=0, d=-1, and b+c+d = 0

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The equation can be simplified as,

x ( x + 1 ) ( x 1 ) ( x + 1 ) ( x 2 x + 1 ) = 1 x 3 x 2 + x = x 1 x 3 x 2 + 1 = 0 \dfrac{x}{(x+1)(x-1)}\cdot(x+1)(x^2-x+1)=1\\ \implies x^3-x^2+x=x-1\\ \implies x^3-x^2+1=0

On comparing with the given general equation, we have,

b = ( 1 ) , c = 0 , d = 1 b + c + d = 0 b=(-1)~,~c=0~,~d=1\implies \boxed{b+c+d=0}

Prasun Biswas - 6 years, 4 months ago

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upvoted :)

Mahtab Hossain - 6 years, 1 month ago

If b = 1 , c = 0 , d = 1 b=-1,c=0,d=-1 then b + c + d = 2 b+c+d=-2

William Isoroku - 6 years, 4 months ago

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