Use cross product formula in R^4 to obtain a vector that is orthogonal to rows of A Please help with first part and check if i answered the questions correctly. The matrix A = 1 4 -1 2 0 1 0 -1 2 9 -2 2 1. Use cross product formula in R^4 to obtain a vector that is orthogonal to the rows of A. I multiply the matrix A by a 4x1 matrix X and equate to 0. Matrix X = x1 x2 x3 x4 Then i get: x1+ 4x2 - 3x3 + 2x4 =0 x2 + x4 = 0 2x1 + 9x2 - 2x3 + 2x4 =0 x1 = -4x2 + 3x3 - 2x4 x2 = - x4 x3 = x3 2x4 = -2x1- 9x2 + 2x3 And then... i'm stuck. 2. How is this vector related to the null space of A? My answer: That vector is perpendicular to the null space of A. Is this correct and is there another way to put it?