If ` vec R = (vec A = vec B), show that ` R^(2) =A^(2) +B^(20 +2 AB cos theta` wher, ` theta` is the smaller angle between `vec A and vec B`.

Explanation

Given ` vec `R = (vec A + vec B) , Taking dot product of ` R` with itself , we have,
` vec R .vec R = ( vec A+ vec B). ( vec A+ vec B)`
or ` R^2 = vec A. vec A + 2 vec A.vec B + vec B. vec B`
or ` R^2 = A^2 + 2 AB cos theta + B^2`.