Let A(1, 0), B(2, -1) and C ( 73, 43 ) be three points. If the equation of the bisector of the angle ABC is x + y = 5, then the value of 2 + 2 is
- 5
- 10
- 8
- 13
Answer
(2) 10
Solution
The bisector of angle ABC passes through B along the sum of the unit vectors along BA and BC.
Here BA = (-1, 1) with | BA| = 2, and BC = ( 13, 73 ) with | BC| = 503 = 5 23, so the unit vectors are 1 2(-1, 1) and 15 2(1, 7).
Hence the direction of the bisector 15 2 [(-5, 5) + (1, 7) ] (-4, 12) (-1, 3), so its slope is -3 and the line through B(2, -1) is
y + 1 = -3(x - 2)
3x + y = 5
So = 3 and = 1.
2 + 2 = 9 + 1 = 10
Answer: (2)