Ques. 1JEE Main 2024, 27 January (Morning Shift)
If (a, b) be the orthocentre of the triangle whose vertices are (1,2),(2,3) and (3,1), and I1= ab x (4x-x2 )dx, I2= ab (4x-x2 )dx, then 36 I1I2 is equal to :
- 80
- 72
- 66
- 88
Answer
(2) 72
Solution
Slope of AB= 3-22-1=1 altitude from C(3,1): y-1=-(x-3), i.e. x+y=4
[figure]
Orthocentre H(a, b) lies on this altitude a+b=4
King rule: x a+b-x=4-x, and 4x-x2=x(4-x) is unchanged
I1= ab(4-x) (4x-x2 )dx
Adding the two forms: 2I1=4I2 I1I2=2
36 I1I2=72
Answer: (2)