The length of a diagonal on a square represents a hypotenuse of the right triangle whose legs are equal And also this triangle is a half of the square The length of one side of a square = 90 feet
∴ d² = 90² + 90² = 2 * 90² ∴ d = 90√2
∴ The equations can be used to calculate d = 90√2
In general for any square has length of side = x The diagonal of the square = d = x√2