1. The problem is to simplify the expression $2,5\sqrt{2}$. 2. First, note that the comma in $2,5$ is a decimal separator, so this is $2.5\sqrt{2}$. 3. The expression means $2.5$ multiplied by the square root of $2$. 4. The square root of $2$ is approximately $1.414$. 5. Multiply $2.5 \times 1.414$ to get the approximate value. 6. $$2.5 \times 1.414 = 3.535$$ 7. Therefore, $2,5\sqrt{2} = 3.535$ approximately.