Let A(-1, 1) and B(2, 3) be two points and P be a variable point above the line AB such that the area of PAB is 10. If the locus of P is ax + by = 15, then 5a + 2 b is :
- - 125
- - 65
- 6
- 4
Answer
(1) - 125
Solution
Let P(h, k): area = 12 vmatrix h & k & 1 \ -1 & 1 & 1 \ 2 & 3 & 1 vmatrix = 12|-2h + 3k - 5|
P is above AB (2x - 3y + 5 = 0) -2h + 3k - 5 > 0
12(-2h + 3k - 5) = 10 -2x + 3y = 25
- 65x + 95y = 15 a = - 65, b = 95
5a + 2b = -6 + 185 = - 125
Answer: (1)