Evaluate :
`5x^(3)y^(4) ` when x=2 ,y=-1

Answer

To evaluate the expression \( 5x^3y^4 \) when \( x = 2 \) and \( y = -1 \), we will follow these steps:

### Step 1: Substitute the values of \( x \) and \( y \)
We start by substituting the given values into the expression:
\[ 5x^3y^4 = 5(2)^3(-1)^4 \]

### Step 2: Calculate \( x^3 \) and \( y^4 \)
Next, we calculate \( (2)^3 \) and \( (-1)^4 \):
\[ (2)^3 = 2 \times 2 \times 2 = 8 \]
\[ (-1)^4 = (-1) \times (-1) \times (-1) \times (-1) = 1 \]
(Note: Since the negative number is raised to an even power, the result is positive.)

### Step 3: Substitute back into the expression
Now, we substitute these results back into the expression:
\[ 5(2)^3(-1)^4 = 5 \times 8 \times 1 \]

### Step 4: Multiply the numbers
Finally, we perform the multiplication:
\[ 5 \times 8 \times 1 = 40 \]

### Final Answer
Thus, the value of the expression \( 5x^3y^4 \) when \( x = 2 \) and \( y = -1 \) is:
\[ \boxed{40} \]