A diagonal of a parallelogram divides it into two congruent triangles.
True
Suppose ABCD is a parallelogram and BD is the diagonal.
There are two triangles - Δ ABD and Δ CDB
In Δ ABD and Δ CDB,
AD = BC (opposite sides of a parallelogram are equal)
AB = CD (opposite sides of a parallelogram are equal)
BD is common
∴ By SSS criterion of congruency,
Δ ABD ≅ Δ CDB
Hence, the given statement is true.