## Trending News

Promoted

# Vector,alegebra question , please explain the answer?

In Vectors why does

(a+b)^2 = a^2+b^2-2(a)(b)cos thetha

where does the there come from ?

Update:

still where does the cos come from ? I times As and Bs and cos comes from nowhere

### 1 Answer

Relevance

- TheSicilianSageLv 71 decade agoFavorite Answer
The law of cosines

See: http://www.themathpage.com/aTrig/law-of-cosines.ht...

The method is to break any triangle into 2 right triangles

... drop an altitude from the tip of the smallest side (next to the angle)

to the "base" (which is the larger side next to the angle) and do the math.

Still have questions? Get your answers by asking now.