The value of x in terms of l is

Data given;
Length = l
width = 2l
diagonal = x
assuming we cut a section across the diagonal, we would have a right angle triangle. we can solve the right angle triangle using Pythagoras Theorem.
<h3>Pythagoras Theorem</h3>
This formula is used to find the missing side of a right angle triangle where x is equal to it's longest side i.e the hypothenuse.
The square of the hypothenuse is equal to the sum of the square of it's two sides.
substituting the values

From the calculation above, we have x in terms of l as

Learn more on rectangles and Pythagoras theorem here;
brainly.com/question/654982