Answer:
Pythagorean theorem: In a right triangle, the square of the hypotenuse is equal to the sum of squares on the other two sides.
here we will apply the Pythagorean reciprocal (to check if the triangle is right): In a triangle, if the square of one side is equal to the sum of the squares of the other 2 sides, then this triangle is right.
51, 68, 85
if 85²=51²+68², then the lengths form a right triangle
85²=7225
68²+51²=7225
according to the Pythagorean reciprocal the triangle formed by these 3 lengths is right