SOLUTION: Consider the following. x3 − kx2 + 2kx − 18 Find the value of k such that x − 3 is a factor of the above.

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Question 1128287: Consider the following.
x3 − kx2 + 2kx − 18
Find the value of k such that x − 3 is a factor of the above.

Found 3 solutions by josgarithmetic, MathLover1, MathTherapy:
Answer by josgarithmetic(39620) About Me  (Show Source):
You can put this solution on YOUR website!
Performing synthetic division for root or zero of 3, the remainder is 9-3k, which must be 0.

9-3k=0
9=3k
highlight%283=k%29

Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!
x%5E3+-+kx%5E2+%2B+2kx+-18
Find the value of k such that x-3 is a factor of the above.
We should attempt synthetic division to find when
%28x%5E3+-+kx%5E2+%2B+2kx+-18%29%2F%28x-3%29has a remainder of 0, which would signify that it is a factor of the polynomial.
The synthetic substitution would be set up as:
3| 1.....-k.....2k...-18

------------------------------------------------------|0
Treating the synthetic division like any other synthetic division problem, we see that
3| 1.....-k..........2k.................-18
−----------3........-3k%2B9.........-3k%2B27
−−---------1.....-k%2B3........-k%2B9.......|0

If the remainder equals 0, then we know that
-3k%2B27-18=0
27-18=3k
3k=9
k=3

x%5E3+-+3x%5E2+%2B+2%2A3x+-18
x%5E3+-+3x%5E2+%2B+6x+-18
x%5E3+-+3+x%5E2+%2B+6+x+-+18+=+%28x%5E2+%2B+6%29+%2A+%28x+-+3%29+%2B+0

Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!

Consider the following.
x3 − kx2 + 2kx − 18
Find the value of k such that x − 3 is a factor of the above.
Set the expression equal to 0, as follows: matrix%281%2C3%2C+x%5E3+-+kx%5E2+%2B+2kx+-+18%2C+%22=%22%2C+0%29
One factor: x - 3 signifies that 1 of its roots is 3.
All you have to do is substitute 3 for x, and you'll see that k = 3.
That's all! Nothing MORE, nothing LESS!!