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Divide f(x) = x cubed - 4x squared + 2x + 7 by (x - 3). What remainder does the Remainder Theorem give?
AA remainder of 0
BA remainder of 7
CA remainder of 10
DA remainder of 4
Answer & Solution
Correct answer: D. A remainder of 4
1. The Remainder Theorem says that dividing by x minus k leaves the remainder f(k).
2. Here the divisor is x - 3, so k is 3.
3. Evaluate f(3), starting with 3 cubed, which is 27.
4. Next comes negative 4 times 9, which is negative 36.
5. Next comes 2 times 3, which is 6, and finally the constant 7.
6. Adding gives 27 minus 36 plus 6 plus 7, which is 4.
7. So the remainder is 4, and it is not 0, so x - 3 is not a factor.
8. A remainder of 0 would assume the divisor is a factor without testing it.
9. A remainder of 7 reads off the constant term instead of evaluating at 3.
10. A remainder of 10 comes from using k equal to negative 3 by mistake.
_Source: OpenStax Precalculus (CC BY 4.0), section 3.6 Zeros of Polynomial Functions_
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