Matrix Algebra Review

This video reviews some basic results related to eigenvalues and eigenvectors that are related to Principal Component Analysis

[tessashen]

Thanks for this video series, this has been incredible to learn with clear instruction. At 11:56 where a1 and a2 are calculated I am unable to get the same coordinates which you have presented [-4, 1]. instead i have calculated [4, -1].

here are my workings

calc determ of B: (1x1)-(3x2)=-5

B^-1 = (-1/5)*(1, -3, -2, 1)

B^-1 = [-0.2, 0.6, 0.4, -0.2] (then multiply by [1, 7])

[ -0.2*1+0.6*7, 0.4*1 + -0.2*7]

=[4, -1]

not sure where i am going wrong. any help would be greatly appreciated.