`sqrt(20a) xx sqrt(5a)` , assuming a is positive.

Answer

To solve the expression \( \sqrt{20a} \times \sqrt{5a} \), we can follow these steps:

### Step 1: Combine the square roots
Using the property of square roots that states \( \sqrt{x} \times \sqrt{y} = \sqrt{x \times y} \), we can combine the two square roots:

\[ \sqrt{20a} \times \sqrt{5a} = \sqrt{(20a) \times (5a)} \]

### Step 2: Multiply the expressions inside the square root
Now, we will multiply the expressions inside the square root:

\[ (20a) \times (5a) = 20 \times 5 \times a \times a = 100a^2 \]

### Step 3: Take the square root
Next, we take the square root of the result from Step 2:

\[ \sqrt{100a^2} \]

### Step 4: Simplify the square root
We can simplify the square root:

\[ \sqrt{100} \times \sqrt{a^2} = 10 \times a \]

### Final Answer
Thus, the final result is:

\[ 10a \]

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