Both parallelogram and triangular method are used to find the resultant vector of two or more vectors.

In the triangular method, we placed the initial point of the second vector on the terminal point of the first vector and then drew the resultant from the initial point of the first vector to the terminal point of the second vector.

Where as in parallelogram method, we placed the initial points of the two vectors together, then draw the parallel lines to the both of the vectors and resultant is the diagonal of the parallelogram.

Triangle method:

Parallelogram method: