In an equilateral triangle PQR, let the vertex P be at (3, 5) and the side QR be along the line x+y=4. If the orthocentre of the triangle PQR is ( , ), then 9( + ) is equal to:
- 16
- 27
- 36
- 48
Answer
(4) 48
Solution
[figure]
Let M be the foot of the perpendicular from P(3, 5) to x+y-4=0:
x-31= y-51=- 3+5-412+12=-2 M(1, 3)
The triangle is equilateral, the median PM is also an altitude and the orthocentre H = centroid G.
G divides PM in the ratio 2:1
H= ( 3+2 13, 5+2 33 )= ( 53, 113 )
9( + )=9 163=48
Answer: (4)