What is the Law of parallelogram of two vector additions?

If two vectors are represented by two adjacent sides of parallelogram then diagonal of parallelogram through their common point will give the resultant of that vector in magnitude and direction.

Angle between vector tan α = Q Sin Ɵ / P + Q Cos Ɵ

If two vector are in same direction Ɵ = 0
R = P + Q

If two vectors are opposite to each other Ɵ = 180⁰
R = P – Q

If two vectors are right angle to each otherƟ = 90⁰
R =