Creating a diagonal line in a rectangle will create two right triangles. It's given that the length is 6 inches and the width is 5 inches, and the diagonal length itself is missing. We need to use the Pythagorean Theorem here to figure out what this missing length is. The theorem is:

a^2 + b^2 = c^2

"a" and "b" can be interchangeably used to represent length or width. And "c" represents the missing length. So let's plug these numbers in:

(6)^2 + (5)^2 = c^2

36 + 25 = c^2

61 = c^2

Taking the square root of c^2 = 61, we will get:

c = **√61** <-- This is the value of the length of the diagonal.