Question

How do you use vectors to find the interior angles (in radians) of a triangle with the vertices (1,2) (3,4) and (2,5)?

Answer 1

Let the vertices be `A(1,2), B(3,4), & C(2,5).`

Then vector`vec(AB)` `=(2,2),` since,

vector`vec(AB)`=(position vector of `B`) - (position vector of `A`)

`=(3,4)-(1,2)= (3-1,4-2)=(2,2)`

Similarly, vector `vec(BC)=(-1,1),` & vector `vec(CA)=(-1,-3).`