Evaluate :
`9^((5)/(2)) - 3xx8^(0)-((1)/(81))^(-(1)/(2))`

Answer

To evaluate the expression \( 9^{\frac{5}{2}} - 3 \times 8^{0} - \left(\frac{1}{81}\right)^{-\frac{1}{2}} \), we can break it down step by step.

### Step 1: Evaluate \( 8^0 \)
Any number raised to the power of 0 is equal to 1. Therefore:
\[ 8^{0} = 1 \]
So, the expression simplifies to:
\[ 9^{\frac{5}{2}} - 3 \times 1 - \left(\frac{1}{81}\right)^{-\frac{1}{2}} \]

### Step 2: Substitute the value of \( 8^0 \)
Now substituting the value we found:
\[ 9^{\frac{5}{2}} - 3 - \left(\frac{1}{81}\right)^{-\frac{1}{2}} \]

### Step 3: Evaluate \( 9^{\frac{5}{2}} \)
We can rewrite \( 9 \) as \( 3^2 \):
\[ 9^{\frac{5}{2}} = (3^2)^{\frac{5}{2}} = 3^{2 \times \frac{5}{2}} = 3^5 \]
Calculating \( 3^5 \):
\[ 3^5 = 3 \times 3 \times 3 \times 3 \times 3 = 243 \]
So now our expression is:
\[ 243 - 3 - \left(\frac{1}{81}\right)^{-\frac{1}{2}} \]

### Step 4: Evaluate \( \left(\frac{1}{81}\right)^{-\frac{1}{2}} \)
We can rewrite \( \frac{1}{81} \) as \( 81^{-1} \), so:
\[ \left(\frac{1}{81}\right)^{-\frac{1}{2}} = 81^{\frac{1}{2}} = \sqrt{81} = 9 \]
Now substituting this back into the expression:
\[ 243 - 3 - 9 \]

### Step 5: Simplify the expression
Now we can simplify:
\[ 243 - 3 = 240 \]
Then:
\[ 240 - 9 = 231 \]

### Final Answer
Thus, the value of the expression is:
\[ \boxed{231} \]