Hello,
can anyone explain the second one? I can obviously understand the first one,
however, the teacher didn’t tell us why the second one is valid.
If the second one doesn’t convince me, then I can’t really understand the cosine one, which is the third equation.
This is only valid in the special case that u and v are aligned.
And the case <u,u> is of course the special case where both vectors are aligned and have the same length,
The fact is that the cosine equation is the proper definition… the special cases (like the two shown) derive from that one.
