ABCD is a parallelogram. Express through vectors AB and AD vector AC, vector DB.

Given: parallelogram ABCD, vector AB, vector AD.
Express: vector AC, vector DB.
Solution:
Using the vector addition method according to the parallelogram rule (vectors AB and AD come from the same point, the sum vector comes from a common starting point and is the parallelogram diagonal), we get:
vector AB + vector AD = vector AC.
According to the triangle rule (the end of the vector (- AD) coincides with the beginning of the vector AB, their sum is a vector, the beginning of which coincides with the beginning of the vector (- AD), and the end coincides with the end of the vector AB) we get:
vector AB – (vector AD) = vector DB.