prove that the 4 triangles into which the diagonals of a rhombus divide it are congruent
Let there be a rhombus ABCD in which O is the mid point where the diagonals intersect
Since the diagonals of a rhombus intersect each other AO = OC and BO = OD
Also in the rhombus all sides are equal
hence all the four triangles formed are congruent by SSS congruence.