Thursday, August 25, 2011

What is the value of k for which when x^3 - 2x^2 + 3kx + 18 is divided by (x - 6), the remainder is equal to zero?

You should write the factored form of polynomial such
that:


`x^3 - 2x^2 + 3kx + 18 = (x - 6)(ax^2 + bx +
c)`


You need to open the brackets to the right side such
that:


`x^3 - 2x^2 + 3kx + 18 = ax^3 + bx^2 + cx - 6ax^2 -
6bx - 6c`


You need to collect like terms to the right side
such that:


`x^3 - 2x^2 + 3kx + 18 = ax^3 + x^2(b - 6a) +
x(c - 6b) - 6c`


Equating coefficients of like powers
yields:


`a = 1`


b - 6a = -2
=> b - 6 = -2 => b = 4


`c - 6b = 3k =gt c -
24 = 3k =gt c = 3k + 24`


`-6c = 18 =gt c =
-3`


You need to substitute -3 for c in `c = 3k + 24`  such
that:


`-3 = 3k + 24`


Dividing
by 3 both sides yields:


`-1 = k + 8 =gt k =
-9`


Hence, evaluating k using th factored
form of polynomial yields `k = -9` .

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