Show that the dot product of vectors a and b is equal to 1/4|a+b|^2 - 1/4|a-b|^2
a dot b = |a||b|cos(theta)
a dot b = a1b1 + a2b2 + ...
The Attempt at a Solution
I've tried using the combination of the cosine law and those two above dot product equations and I have gotten no where. Any help would be greatly appreciated. (: