91影视

a) If the plane contains the origin, $\stackrel{炉}{v_1}$and $\stackrel{炉}{v_2}$are from the plane, but not parallel, and $\stackrel{炉}{v_3}=\stackrel{炉}{v_1}脳\stackrel{炉}{v_2}$, then the three vectors make for a positively oriented basis, but they'll reflect into $\stackrel{炉}{v_1},\stackrel{炉}{v_2}\mathrm{and}\stackrel{炉}{{\mathrm{v}}_3}$respectively, and this basis is negatively oriented.

So, this reverses orientation.

b) If the line contains the origin,$\stackrel{炉}{v_1}$and$\stackrel{炉}{v_2}$are orthogonal to the line, but not parallel, and$\stackrel{炉}{v_3}=\stackrel{炉}{v_1}脳\stackrel{炉}{v_2}$, then the three vectors make for a positively oriented basis.

They'll reflect into $\stackrel{炉}{v_1},\stackrel{炉}{v_2}\mathrm{and}\stackrel{炉}{{\mathrm{v}}_3}$, respectively.

This basis is once again positively oriented, so this preserves orientation.

c) This transforms every vector $\stackrel{鈫�}{x}$into$-\stackrel{鈫�}{x}$, so for any positively oriented basis $\stackrel{炉}{v_1},\stackrel{炉}{v_2}\mathrm{and}\stackrel{炉}{{\mathrm{v}}_3}$the basis $\stackrel{炉}{v_1},\stackrel{炉}{v_2},\stackrel{炉}{{\mathrm{v}}_3}$is negatively oriented.

Thus, this reverses orientation.