<p>The term independent of x in the expansion of <span class="math-tex">\(\left(\frac{1}{60}-\frac{x^{8}}{81}\right) \cdot\left(2 x^{2}-\frac{3}{x^{2}}\right)^{6}\)</span> is equal to</p>
<p style="display:inline">-36</p>
<p style="display:inline">36</p>
<p style="display:inline">-72</p>
<p style="display:inline">-108</p>
Step-by-Step Solution
Key Concept: Identify the term independent of x by distributing the binomial expansion's general term and solving for r values that make the combined exponent of x equal to zero for each separate product.
Step 1: Find the general term of the binomial expansion $\left(2 x^{2}-\frac{3}{x^{2}}\right)^{6}$.
The general term, $T_{r+1}$, in the expansion of $(a+b)^n$ is given by $T_{r+1} = ^n C_r a^{n-r} b^r$.
Here, $a = 2x^2$, $b = -\frac{3}{x^2}$, and $n=6$.
$$T_{r+1} = ^{6} C_{r}\left(2 x^{2}\right)^{6-r}\left(-\frac{3}{x^{2}}\right)^{r}$$
Step 2: Simplify the general term to find the power of $x$.
$$T_{r+1} = ^{6} C_{r}(2)^{6-r}(x^2)^{6-r}(-3)^{r}(x^{-2})^{r}$$
$$T_{r+1} = ^{6} C_{r}(-3)^{r}(2)^{6-r} x^{2(6-r)} x^{-2r}$$
$$T_{r+1} = ^{6} C_{r}(-3)^{r}(2)^{6-r} x^{12-2r-2r}$$
$$T_{r+1} = ^{6} C_{r}(-3)^{r}(2)^{6-r} x^{12-4r}$$
Step 3: Decompose the given expression to find the term independent of $x$.
The given expression is $\left(\frac{1}{60}-\frac{x^{8}}{81}\right) \cdot\left(2 x^{2}-\frac{3}{x^{2}}\right)^{6}$.
To find the term independent of $x$, we consider two parts:
1. The term independent of $x$ in $\frac{1}{60}\left(2 x^{2}-\frac{3}{x^{2}}\right)^{6}$.
2. The term independent of $x$ in $-\frac{x^{8}}{81}\left(2 x^{2}-\frac{3}{x^{2}}\right)^{6}$.
Step 4: Calculate the term independent of $x$ for the first part: $\frac{1}{60} \cdot T_{r+1}$.
For this term to be independent of $x$, the power of $x$ in $T_{r+1}$ must be $0$.
So, we set the exponent of $x$ from Step 2 to zero:
$12-4r = 0 \implies 4r = 12 \implies r=3$.
Substitute $r=3$ into the general term $T_{r+1}$ and multiply by $\frac{1}{60}$:
Term$_1 = \frac{1}{60} \cdot ^{6} C_{3}(-3)^{3}(2)^{6-3}$
Term$_1 = \frac{1}{60} \cdot \frac{6 \times 5 \times 4}{3 \times 2 \times 1}(-3)^{3}(2)^{3}$
Term$_1 = \frac{1}{60} \cdot 20 \cdot (-27) \cdot 8$
Term$_1 = \frac{1}{3} \cdot (-27) \cdot 8$
Term$_1 = -9 \cdot 8 = -72$.
Step 5: Calculate the term independent of $x$ for the second part: $-\frac{x^{8}}{81} \cdot T_{r+1}$.
For this term to be independent of $x$, the total power of $x$ must be $0$. The $x$ term in $-\frac{x^8}{81} \cdot T_{r+1}$ is $x^8 \cdot x^{12-4r}$.
So, we set the total exponent of $x$ to zero:
$8 + (12-4r) = 0$
$20 - 4r = 0 \implies 4r = 20 \implies r=5$.
Substitute $r=5$ into the general term $T_{r+1}$ and multiply by $-\frac{1}{81}$:
Term$_2 = -\frac{1}{81} \cdot ^{6} C_{5}(-3)^{5}(2)^{6-5}$
Term$_2 = -\frac{1}{81} \cdot 6 \cdot (-243) \cdot 2$
Note that $243 = 3^5$ and $81 = 3^4$.
Term$_2 = -\frac{1}{3^4} \cdot 6 \cdot (-3^5) \cdot 2$
Term$_2 = -1 \cdot 6 \cdot (-3) \cdot 2$
Term$_2 = 18 \cdot 2 = 36$.
Step 6: Sum the terms independent of $x$ from both parts.
The total term independent of $x$ is the sum of Term$_1$ and Term$_2$:
Total term = Term$_1$ + Term$_2$
Total term = $-72 + 36 = -36$.
The final answer is $\boxed{-36}$.
Correct Answer: A