Let f be a function such that 3f(x) + 2f ( m19x ) = 5x, x 0, where m = i=19 (i)2. Then f(5) - f(2) is equal to
- 36
- 9
- -9
- 18
Answer
(4) 18
Solution
m = i=19 i2 = 9 10 196 = 285
m19 = 15
3f(x) + 2f ( 15x ) = 5x ...(i)
Replacing x by 15x:
3f ( 15x ) + 2f(x) = 75x ...(ii)
3 (i) - 2 (ii):
9f(x) - 4f(x) = 15x - 150x
f(x) = 3x - 30x
f(5) = 15 - 6 = 9 and f(2) = 6 - 15 = -9
f(5) - f(2) = 9 - (-9) = 18
Answer: (4)