4. write v=(2,5,-4,0) as a linear combination of u, =(1,3,2,1), u_2=(2-1, 3,6), if possible. u_3=(2,-2,-5,4), and

Identify all the cases where non-probability sampling is used when attempting to study the characteristics of a large city. studies on every subject in the population divide a population in groups and obtain a sample studies with a limited amount of time demonstrate existing traits in a population studies with the nth person selected