Let a triangle PQR be such that P and Q lie on the line x+38= y-42= z+12 and are at a distance of 6 units from R(1, 2, 3). If ( , , ) is the centroid of PQR, then + + is equal to :
- 4
- 5
- 6
- 8
Answer
(3) 6
Solution
Any point on the line: (8t-3, 2t+4, 2t-1)
Distance from R(1, 2, 3) is 6: (8t-4)2+(2t+2)2+(2t-4)2=36
72t2-72t+36=36 72t(t-1)=0 t=0 or 1
P(-3, 4, -1), Q(5, 6, 1)
Centroid ( , , )= ( -3+5+13, 4+6+23, -1+1+33 )=(1, 4, 1)
+ + =6
Answer: (3)