Let a variable line of slope m > 0 passing through the point (4, -9) intersect the coordinate axes at the points A and B. The minimum value of the sum of the distances of A and B from the origin is
- 30
- 15
- 10
- 25
Answer
(4) 25
Solution
Line: y + 9 = m(x - 4)
A (4 + 9m, 0 ), B(0, -9 - 4m)
[figure]
m > 0: OA + OB = 4 + 9m + 9 + 4m
= 13 + (4m + 9m )
A.M. G.M.: 4m + 9m 2 36 = 12 (equality at m = 32)
minimum = 13 + 12 = 25
Answer: (4)