questions 1: the three vectors x, y, z have real-valued components and form the sides of a triangle. Prove the Law of Cosines for these vectors, i.e...that

|z|^2 = |x|^2 + |y|^2 - 2*x*y = |x|^2 + |y|^2 - 2*x*y*cos(theta)

where theta is the angle between vectors x and y. (can be using scalar product to solve)

question 2: Let vector x = (1,1,0,0), y = (-1,1,0,0), z = ( 0,0, 1,1), t = (0,0,-1,1). Show that these vectors are linearly independent. Therefore, any subset of them is linearly independent. Discuss the space spanned by each pair of the vectors.

anyone can help ?