V is a subspace of R^4
V={(x, -y, 2x+y, x-2y): x,y E R}
1) extend {(2,-1,5,0)} to a basis of V.
2) find subspace W of R^4 for which R^4= direct sum V(+)W.
solution:
1)the dimension of V is 2.therefore i need to add one more vector to (2,-1,5,0).
the 2nd vector is (1,0,2,1)...