Monday, August 25, 2014

Determine the remainder if f=3x^4-2x^3+x^2+ax-1 is divided by (x-1)^2.

We'll write the division with
reminder:


f(x) = (x-1)^2*C(x) +
R(x)


Since the divisor is a polynomial of second order, the
reminder is a polynomial of first order.


R(x) = mx +
n


We'll calculate f(1):


f(1) =
(1-1)^2*C(1) + R(1)


f(1) =
R(1)


We'll determine f(1), substituting x by 1 in the given
expression of polynomial f:


f(1) =
3-2+1+a-1


f(1) = 1 + a


R(1) =
m + n


m + n = 1+a (1)


Now,
we'll calculate the first derivative of f(x):


f'(x) =
(3x^4-2x^3+x^2+ax-1)'


f'(x) = 12x^3 - 6x^2 + 2x +
a


f'(x) = [(x-1)^2*C(x) +
R(x)]'


f'(x) = 2(x-1)*C(x) + (x-1)^2*C'(x) +
R'(x)


f'(x) = 2(x-1)*C(x) + (x-1)^2*C'(x) +
m


f'(1) = m


f'(1) = 12 - 6 + 2
+ a


m = 8 + a (2)


We'll
substitute (2) in  (1):


1+a = 8 + a +
n


We'll subtract 8 + a:


n = 1
+ a - 8 - a


We'll eliminate and combine like
terms:


n =
-7


The reminder R(x)
is:


R(x) = (8 + a)x -
7

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