I'm not sure how to do part a) and b). For a) I don't get how the hint helps.
Eg, I did $\displaystyle P_1P_2 = \frac{1}{||a||^2}aa^T\frac{1}{||b||^2}bb^T$ and we know that a.b = 0 but there are no dot products in the former equation...
I'm not sure how to do part a) and b). For a) I don't get how the hint helps.
Eg, I did $\displaystyle P_1P_2 = \frac{1}{||a||^2}aa^T\frac{1}{||b||^2}bb^T$ and we know that a.b = 0 but there are no dot products in the former equation...
In fact, there is a (disguised) dot product in that equation, because $\displaystyle a^{\textsc t}b$ is just another way of writing $\displaystyle a.b$.