Tuesday, March 8, 2011

Given that (x-2) and (x+3) are factors of 2x4-ax3-10x2+bx-54, find a and b.HELP!

The given expression is:


2x^4
- ax^3 -10x^2 + bx - 54


As (x - 2) is a factor of the given
expression:


For x = 2 the value of factor (x - 2) = (2 - 2)
= 0


As one factor is 0 the value of the complete expression
is also zero. Therefor substituting value x = 2 in the given expression and equating it
to 0 we get:


2(2^4) - a(2^3) -10(2^2) + b*2 - 54
=54


32 - 8a - 40 + 2b - 54 =
0


- 8a + 2b = 62   ...  
(1)


Similarly:


As (x + 3) is a
factor of the given expression:


For x = -3 the value of
factor (x + 3) = (- 3 + 3) = 0


As one factor is 0 the value
of the complete expression is also 0. Therefore substituting value x = - 3 in the given
expression and equating it to 0 we get:


2(3^4) - a(3^3)
-10(3^2) + b*(-3) - 54 =54


162 + 27a - 90 - 3b - 54 =
0


27a - 3b = - 18


9a - b = -
6   ...   (2)


Multiplying equation 2 by 2 we
get:


a + 2b = 62


18a - 2b = -
12   ...   (3)


Adding equations (1) and (3) we
get:


- 8a + 18a + 2b - 2b = 62 -
12


10a =
50


Therefore:


a = 50/10 =
5


Substituting this value of a in equation (2) we
get:


9*5 - b = - 6


45 - b = -
6


b = - 6 - 45 = -
51


Answer:


a = 5, and  b = -
51

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