Friday, April 5, 2013

Determine the reminder when f(x)= (x-1)^2 + x^5 + x^4 - x^2 + 2x is divided by g(x)=x^3+3x^2+3x+1 ?

We'll expand the square from
f(x):


f(x) = x^2 - 2x + 1 + x^5 + x^4 - x^2 +
2x


We'll eliminate like
terms:


f(x) = x^5 + x^4 +
1


We'll recognize in expression of g(x) the binomial raised
to cube:


g(x) = (x+1)^3


Since
the divisor is of 3rd order, the reminder has to be of 2nd
order.


r=ax^2 + bx + c


We 'll
write the reminder theorem:


f=g*q + r, where q is the
quotient of the division.


We notice that x=1 is a multiple
root of the polynomial g.


f(-1)=g(-1)*q(-1) +
r(-1)


By substituting the value x=-1 into all polynomials,
we'll obtain:


f(-1)= (-1)^5 + (-1)^4 +
1


f(-1)=-1+1+1


f(-1)=1


g(-1)=
(-1+1)^3=0


r(-1)=a-b+c


So,
we'll have:


1=0*q(-1) +
a-b+c


1=a-b+c


Because of the
fact that x=-1 is a multiple root, it will cancel the first derivative of the
expression: f=g*c + r


f' =(g*c)' +
r'


5x^4 +4 x^3=3*(x+1)^2*q+(x+1)^3*q' +2*ax+
b


By substituting the value x=-1 into all polynomials,
we'll
obtain:


5-4=-2*a+b


1=-2*a+b


We'll
calculate the first derivative of the expression


5x^4 +4
x^3=3*(x+1)^2*q+(x+1)^3*q' +2*ax+ b


(5x^4 +4
x^3)'=(3*(x+1)^2*q+(x+1)^3*q' +2*ax+ b)'


5*4* x^3 + 4*3*
x^2=6*(x+1)*q+3*(x+1)^2*q'+3*(x+1)^2*q'+(x+1)^3*q"+2a


By
substituting the value x=-1 into all polynomials, we'll
obtain:


-20+12=2*a


We'll
divide by 2:


a = -10 + 6


a =
-4


-2a+b=1


-2*(-4) + b =
1


b = 1 - 8


b =
-7


a-b+c =
1


-4+7+c=1


3+c=1


c=1-3


c=-2


The
reminder is: r(x) = -4x^2 - 7x - 2.

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