The Broom Riddle (Solution) ft. Kurt Hugo Schneider part 3/3

Addition of angles of C and B gives a (1,3) vector which gives the same negative angle as (1,-3). Also A gives a (3,1) vector. Using simple vector rules we find that (3,1) and (1,-3) are perpendicular. Which means they all add up to 90 and c alone is 45 which means a plus b is 45.
You can find angle c plus b by using the diagonals of the small squares on the grid. On top of the line c, imagine that line c is the base and draw a 2,1 vector on top of it using the diagonals of the squares. Then find the new vectors which is 1,3 but start from the the beginning of line c