If we need to measure distance across a lake, it will be hard to get an accurate measurement as we cannot walk on water.
However, we can measure the angle between an elevated position and the other side of the lake, and we can then replicate the angle to the ground's side. By doing this, we can construct triangles with two pairs of congruent angles and one pair of congruent included sides.
By the ASA Congruence Theorem, the triangles above are congruent. We can measure the distance across the lake by measuring the side of the second triangle that's along the ground.
