Need help, test coming soon!

Need explanations!

My test is coming up real soon!

Need help with these questions.

Sorry for the rudeness (Doh) ... tests make me... nervous...

Describe all vectors v = [x,y] that are orthogonal to u = [a,b].

And I really really need help understanding "span" in linear algebra. How do you determine if a vector is the span of a matrix?

prob) determine if the vector b is in the span of the columns of the matrix A.

A =

[1 2]

[3 4]

b =

[5]

[6]

prob) show that R^2 =

span

([1] , [1])

([1] , [-1])