Let the mid points of the sides of a triangle ABC be ( 52, 7 ), ( 52, 3 ) and (4, 5). If its incentre is (h, k), then 3h+k is equal to :
- 11
- 12
- 13
- 14
Answer
(3) 13
Solution
Let the mid-points be D ( 52,7 ), E ( 52,3 ), F(4,5).
Each vertex = sum of the two adjacent mid-points minus the opposite one:
E+F-D=(4,1), D+F-E=(4,9), D+E-F=(1,5)
Take A(1,5), B(4,9), C(4,1):
a=BC=8, b=CA= 9+16=5, c=AB= 9+16=5
Incentre = ( ax1+bx2+cx3a+b+c, ay1+by2+cy3a+b+c )
h= 8(1)+5(4)+5(4)18= 4818= 83
k= 8(5)+5(9)+5(1)18= 9018=5
∴ 3h+k=8+5=13
Answer: (3)