Planned Comparisons, Vectors, and Variance

You have two planned comparisons’ vectors: [-1,-1,2] and [-1,0,1]. What is the angle between these two vectors (in degrees) and what does this mean for their variance?

I managed to find that the angle was 30 degree by using the dot product formula and that these planned comparisons were not orthogonal, but I didn't understand what could be said about their variance. Could you please explain it in simple terms for me?