Find x in x^3+x^2-x-1=0 Equation

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SUMMARY

The equation x^3 + x^2 - x - 1 = 0 has a known solution at x = 1, indicating that (x - 1) is a factor. By applying Horner's rule or polynomial long division, the remaining quadratic factor can be determined. The coefficients A and B can be solved by equating them to the corresponding coefficients of the original polynomial, leading to a quadratic equation that can be solved for the other roots. While a general cubic formula exists, it is complex and not necessary for this specific problem.

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superelf83
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simple "find the x" question

how do you solve for x in this equation?

x^3+x^2-x-1=0

i know one of them is 1. but the other one...?
 
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If you know that x = 1 is a solution, then (x-1) is a factor of the polynomial. Factor it out and determine the remaining (quadratic) factor, e.g. using Horner's rule.
 
Another way to get the quadratic that is left is to write:
(x- 1)(x2+ Ax+ B)= x3+ Ax2+ Bx- x2- Ax- B= x3+ (A- 1)x2+ (B-A)x- B= x3+ x2- x- 1. In order for those to be equal for all x, corresponding coefficients must be the same: A- 1= 1, B- A= -1, -B= -1.
Solve for A and B and then solve the quadratic equation.

There is a general "cubic" formula but it is very compliciated.
 

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