If α , β , γ are roots to the equation x 3 − x − 1 = 0 , then evaluate the value of the below expression: 1 − α 1 + α + 1 − β 1 + β + 1 − γ 1 + γ
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1 + x x 3 − 1 ( x − 1 ) ( x 2 + x + 1 ) 1 − x 1 − x 1 + x x 6 x 7 ∑ 1 − x 1 + x = x 3 = x = x = x 2 + 1 + x − x = x 2 + x 3 − x = x 2 ( 1 + x ) − x = − x 4 1 = − x 7 = x 2 + 2 x + 1 = x 3 + 2 x 2 + x = − ∑ x 7 = − ∑ ( x 3 + 2 x 2 + x ) = − [ α 3 + β 3 + γ 3 + 2 ( α 2 + β 2 + γ 2 ) + α + β + γ ] = − [ 3 α β γ + 2 ( − 2 ( α β + β γ + γ α ) ) ] = − ( 3 + 4 ) = − 7
Beautiful solution!
replace x by (x-1)/(x+1) and use vieta's to find sum of roots.
Exactly what I did. It worked!!
Yup, the roots are symmetrical, so we can do so.
That was nice and neat .
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Considering the equation A X 3 + B X 2 + C X + D = 0 given that A=1, B=0, C=-1, D=-1 . Using a vieta's theorem: α + β + γ = A − B = 0 α β + β γ + α γ = A C = − 1 α β γ = A − D = 1 . Then: 1 − α 1 + α + 1 − β 1 + β + 1 − γ 1 + γ ⇒ ( 1 − α ) ( 1 − β ) ( 1 − γ ) ( 1 + α ) ( 1 − β ) ( 1 − γ ) + ( 1 + β ) ( 1 − α ) ( 1 − γ ) + ( 1 + γ ) ( 1 − α ) ( 1 − β ) ⇒ 1 − ( α + β + γ ) + ( α β + β γ + α γ ) − ( α β γ ) 3 − ( α + β + γ ) − ( α β + β γ + α γ ) + 3 ( α β γ ) Substitued: ⇒ ( 1 − 0 + ( − 1 ) − 1 ) 3 − 0 − ( − 1 ) + 3 ( 1 ) = − 7