Polygons that have the same size and shape are called congruent polygons. Congruent polygons can be obtained with either rotation (one polygon is rotated and the second is obtained) or one polygon is the mirror image of the other.
Congruent polygons are also similar, because they have same shape and size, only different position or orientation.
If you proof that the one polygon is rotation of the other or a mirror, than you will proof that those two polygons have the same size and shape.
