Let a and B be nonzero vectors, if (a + b) · B = 2|b|2, and |b ||

Let a and B be nonzero vectors, if (a + b) · B = 2|b|2, and |b ||

(a + b) · B = 2 | B | ^ 2 = AB + B ^ 2 = 2 | a | B | cos θ + | B | ^ 2, then 2 | a | cos θ = | B |
Cos θ = | B | / (2 | a |) and | B ||