If the orthocentre of the triangle formed by the lines 2x + 3y - 1 = 0, x + 2y - 1 = 0 and ax + by - 1 = 0, is the centroid of another triangle, whose circumcentre and orthocentre respectively are (3, 4) and (-6, -8), then the value of |a - b| is .
Answer
16
Solution
On the Euler line the centroid G divides OH (circumcentre O, orthocentre H) in 1 : 2, so G = 2O + H3
G = ( 6 - 63, 8 - 83 ) = (0, 0), so the orthocentre of the first triangle is H(0, 0)
[figure]
A: 2x + 3y = 1, x + 2y = 1 A(-1, 1)
AH has slope -1 and AH BC, so BC has slope 1: - ab = 1 b = -a
CH AB (x + 2y = 1), so CH is y = 2x; it meets 2x + 3y = 1 at C ( 18, 14 )
C on ax - ay = 1: a8 - a4 = 1 a = -8, b = 8
|a - b| = 16
Answer: 16