The base of an isosceles trapezoid is 56 and 104, the side is 30. Find the length of the diagonal of the trapezoid.

An isosceles trapezoid is a trapezoid in which the sides are equal, as well as the angles at its bases. The lengths of the diagonals in an isosceles trapezoid are equal to each other.
The length of the diagonal of an isosceles trapezoid is found by the formula:
d = √ (ab + c ^ 2),
where a is the length of the larger base, b is the length of the smaller base, c is the length of the lateral side.
By condition, a = 104, b = 56, c = 30.
Substitute the data according to the value condition and find the length of the diagonal:
d = √ (104 * 56 + 30 ^ 2) = √ (5824 + 900) = √6724 = 82.
Answer: d = 82.