Question 215 of 480
Find the remainder when 3x3 + 5x2 - 11x + 4 is divided by x + 3
Correct Answer:
C
Explanation
To find the remainder when the polynomial \(3x^3 + 5x^2 - 11x + 4\) is divided by \(x + 3\), we can use the Remainder Theorem. The Remainder Theorem states that if a polynomial \(f(x)\) is divided by \(x - c\), the remainder of that division is \(f(c)\). In our case, we need to find the value of the polynomial when \(x = -3\) (since we are dividing by \(x + 3\), which can be rewritten as \(x - (-3)\)).
### Step-by-Step Explanation
1. **Identify the Polynomial**:
The polynomial we are working with is:
\[
f(x) = 3x^3 + 5x^2 - 11x + 4
\]
2. **Substitute \(x = -3\)**:
We will evaluate \(f(-3)\):
\[
f(-3) = 3(-3)^3 + 5(-3)^2 - 11(-3) + 4
\]
3. **Calculate Each Term**:
- Calculate \((-3)^3\):
\[
(-3)^3 = -27 \quad \Rightarrow \quad 3(-27) = -81
\]
- Calculate \((-3)^2\):
\[
(-3)^2 = 9 \quad \Rightarrow \quad 5(9) = 45
\]
- Calculate \(-11(-3)\):
\[
-11(-3) = 33
\]
- The constant term is \(4\).
4. **Combine All Terms**:
Now, we combine all the calculated values:
\[
f(-3) = -81 + 45 + 33 + 4
\]
5. **Perform the Addition**:
- First, combine \(-81\) and \(45\):
\[
-81 + 45 = -36
\]
- Next, add \(33\):
\[
-36 + 33 = -3
\]
- Finally, add \(4\):
\[
-3 + 4 = 1
\]
6. **Final Result**:
Thus, the remainder when \(3x^3 + 5x^2 - 11x + 4\) is divided by \(x + 3\) is:
\[
\text{Remainder} = 1
\]
### Conclusion
The correct option is **C. 1**.
### Explanation of Other Options:
- **A. -4**: This option is incorrect because it does not match the calculated remainder. The calculations show that the remainder is positive, not negative.
- **B. 4**: This option is also incorrect. While it is a positive number, it does not reflect the actual remainder we calculated.
- **D. -1**: This option is incorrect as well. The calculations clearly show that the remainder is positive and not negative.
### Revision Summary:
- Use the Remainder Theorem to find the remainder of a polynomial divided by a linear factor.
- Substitute the value of \(x\) that makes the divisor zero into the polynomial.
- Carefully calculate each term and combine them to find the final remainder.
- Always double-check calculations to avoid common pitfalls in arithmetic.