How to find the angle between two vector

How to find the angle between two vectors
두 벡터의 각도 구하는 법
V1= 2i+3j
V2= 5i-2j

cos a = DotP( [V1],[V2]) over { norm ([V1]) * norm([V2])

cos a = 4 over ( sqrt(13)*sqrt(29) = 78.12

a = arccos (78.11)