Wednesday, May 30, 2012

factorise the following x^3+x^2+1-x

By error you might have given this cubic equation. But having given the equation it has a solution. Since the question is possed by a high school student this may be beyond the syllabus.


In the theory of equations relating to the cubic equations, you can find how to arrive at the roots of a third degree equations.For  any third degree equation , f(x) = x^3+ax^2+bx+c=0 , if  alpha is a root of it,  then f(alpha) = 0. So, (x-alpha) is a factor of f(x) rremainder theorem.


A 3rd degree equation always has 3 roots, alpha, beta gamma, say. Then f(x) = x^3+ax^2+bx+c = (x-alpha)(x-beta)(x-gamma). So, the right side here,you see the factors which you wanted. But for this,you need to find the roots.


For the given expression, x^2+x^2-x+1 , a=1, b=1,c=-1 and d=1, could be expressed like (x-alpha)(x-beta)(x-gamma), if you find the roots, alpha,beta and gamma of the  cubic equation, x^2+x^2-x+1=0. Futher if you are interested you can feed a =1, b=1 c=-1 and d= 2 to any cubic solving calculator and arrive at  the alpha ,beta and gamma as below:


Alpha =   -1.8392867552141612,


Beta  =  0.41964337760708065 + i* 0.6062907292071992 and


Gamma =  0.41964337760708065 - i* 0.6062907292071992,


where i = (-1)^-(1/2) or square root of minus 1.


By calulator

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