Originally Posted by
pyrosilver Okay I am FLIPPING OUT. I have a math test tomorrow. I have to go to bed in an hour, and I just now learned that I have to be able to derive three separate things!
Please help me. I am seriously distressed.
1. How do I derive the Law of Cosines, vector style? Okay here's what I have...the asterisk (*) means dot in this:
|u-v|^2 = |u|^2 + |v|^2 - 2|u||v|cos theta
(u-v)(u-v) = u * u + v * v - 2 |u||v|cos theta
Where do I go from there? How do I make cos theta equal u * v/ |u||v|??
2. Projection formula w = ( (u*v)/u*u ) u ???? How do I derive that?!?!?!!
3. Double angle formula, sinx = 2cosx sinx .... HOW DO I DO THAT...Here is my start:
h=cosx * w
x=sinx * w
PLEASE HELP my test is TOMORROW, if you guys can't help me I'm doomed