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\( f(3) = 65 \)
Solución
**Synthetic Division Setup**
For the polynomial
\[
f(x)=x^4-16,
\]
write it in full form (including all degrees):
\[
f(x)=1x^4+0x^3+0x^2+0x-16.
\]
The coefficients are:
\[
1,\quad0,\quad0,\quad0,\quad-16.
\]
---
**1. Evaluating \( f(3) \) using Synthetic Division**
We set up synthetic division with \( x=3 \):
- Write the coefficients:
\[
\begin{array}{cccccc}
\text{Root: }3 & | & 1 & 0 & 0 & 0 & -16 \\
\hline
& & 1 & & & & \\
\end{array}
\]
- **Step 1:** Bring down the first coefficient: \(1\).
- **Step 2:** Multiply \(1\) by \(3\) and write the result under the next coefficient: \(1\times3=3\).
Now, add \(0+3=3\).
- **Step 3:** Multiply the new value \(3\) by \(3\): \(3\times3=9\).
Then, add: \(0+9=9\).
- **Step 4:** Multiply \(9\) by \(3\): \(9\times3=27\).
Add: \(0+27=27\).
- **Step 5:** Multiply \(27\) by \(3\): \(27\times3=81\).
Finally, add: \(-16+81=65\).
The bottom row represents the coefficients of the depressed polynomial with the last number as the remainder, which is \(f(3)\).
Thus,
\[
f(3)=65.
\]
---
**2. Evaluating \( f(-3) \) using Synthetic Division**
Use the same coefficients and set \( x=-3 \):
- Coefficients:
\[
1,\quad 0,\quad 0,\quad 0,\quad -16.
\]
- **Step 1:** Bring down the first coefficient: \(1\).
- **Step 2:** Multiply \(1\) by \(-3\): \(1\times(-3)=-3\).
Add: \(0+(-3)=-3\).
- **Step 3:** Multiply \(-3\) by \(-3\): \(-3\times(-3)=9\).
Add: \(0+9=9\).
- **Step 4:** Multiply \(9\) by \(-3\): \(9\times(-3)=-27\).
Add: \(0+(-27)=-27\).
- **Step 5:** Multiply \(-27\) by \(-3\): \(-27\times(-3)=81\).
Add: \(-16+81=65\).
Thus,
\[
f(-3)=65.
\]
---
**3. Evaluating \( f(1-\sqrt{6}) \)**
We now evaluate
\[
f(1-\sqrt{6}) = (1-\sqrt{6})^4 - 16.
\]
While synthetic division can be used with irrational numbers, it is often simpler to compute using the binomial expansion.
Use the formula for \((a-b)^4\) with \( a=1 \) and \( b=\sqrt{6} \):
\[
(1-\sqrt{6})^4 = 1^4 - 4(1^3)(\sqrt{6}) + 6(1^2)(\sqrt{6})^2 - 4(1)(\sqrt{6})^3 + (\sqrt{6})^4.
\]
Now, compute each term:
1. \(1^4 = 1.\)
2. \(- 4(1^3)(\sqrt{6}) = -4\sqrt{6}.\)
3. \(6(1^2)(\sqrt{6})^2 = 6 \times 6 = 36,\) since \((\sqrt{6})^2=6.\)
4. \(- 4(1)(\sqrt{6})^3 = -4(6\sqrt{6}) = -24\sqrt{6},\) because \((\sqrt{6})^3=6\sqrt{6}.\)
5. \((\sqrt{6})^4 = 36.\)
Combine the terms:
\[
(1-\sqrt{6})^4 = 1 - 4\sqrt{6} + 36 - 24\sqrt{6} + 36.
\]
Group similar terms:
- Constants: \(1 + 36 + 36 = 73.\)
- Radical terms: \(-4\sqrt{6} - 24\sqrt{6} = -28\sqrt{6}.\)
Thus,
\[
(1-\sqrt{6})^4 = 73 - 28\sqrt{6}.
\]
Subtract 16:
\[
f(1-\sqrt{6}) = (73 - 28\sqrt{6}) - 16 = 57 - 28\sqrt{6}.
\]
---
**Final Answers**
\[
\begin{aligned}
f(3) &= 65, \\
f(-3) &= 65, \\
f(1-\sqrt{6}) &= 57-28\sqrt{6}.
\end{aligned}
\]
So, the answer for
\[
f(3)=\boxed{65}.
\]
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