In △ ABC, a (2, - 1), B (3,2), C (- 3, - 1), judge the shape of △ ABC

In △ ABC, a (2, - 1), B (3,2), C (- 3, - 1), judge the shape of △ ABC

Vector AB = (1,3) vector AC = (- 5,0) vector BC = (- 6, - 3) cos angle a = vector AB * membrane of vector AC / AB * membrane of vector AC = - 5 / 2 root 5, so a is more than 90 ° and it is an obtuse triangle