Khan Academy on a Stick
Proof of the law of cosines
Proof of the law of cosines to solve for a side of a triangle when 2 sides and an angle are known.
If the above player doesn't work, try this direct link.
Proof of the law of cosines to solve for a side of a triangle when 2 sides and an angle are known.
If the above player doesn't work, try this direct link.