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Homework Statement
Prove the law of cosines: If v and w are vectors in R^2, then
|v-w|^2 = |v|^2 + |w|^2 - 2|v||w|cosθ
where θ is the angle between v and w.
2. Homework Equations /info
|x| refers to length, and not absolute value (If that doesn't make any sense then I must be wrong, but our prof. insisted on only using single lines to define a value as 'length', which can be confusing at times).
The Attempt at a Solution
I got blindsided by this question (missed the lecture..). Even just a starting point, or even an online resource would be greatly appreciated, and to go as far fully providing me with the solution would be extremely helpful (but I suppose possibly detrimental).
Also, the rest of the assignment deals with orthogonal projections, and cross products, as well as distances from points to planes, and lines - do these sort of questions involve the usage of the above law?