How reliable is the graphical method for vector addition and subtraction?

To find the direction in vector subtraction, let's consider (A – B).  We have to use vector addition by rewriting it as A + (–B). Then, this negative vector (–B) will have the same magnitude as B. Only that it will point in the opposite direction. Then we will use the head-to-tail method. Following that, we will place the tail of (–B) at the head of A. The resultant vector from the tail of A to the head of –B will give us both the magnitude and direction of A – B.

Scalar quantities only have magnitude, which makes sense to combine using ordinary algebra. But vector quantities have both magnitude and direction. Due to this directional aspect, vectors must obey special rules of vector algebra. Vectors have to specifically follow the triangle law or the parallelogram law of addition to be represented in the graph format. These graphical methods account for both magnitude and direction. This makes sure that the resultant vector accurately reflects the combined effect of the individual vectors. If we apply ordinary algebra, we won't be able to know the directional information.