If the function f(x) = 3x + x - 3xx3, x R, is continuous at x = 0, then f(0) is equal to :
- 4
- -2
- -4
- 2
Answer
(3) -4
Solution
Expand each term near x = 0:
3x = 3x - 92x3 + , x = x - x36 + , 3x = 1 - 92x2 +
So the numerator = - + (3 + )x + 9 2x2 - ( 92 + 6 )x3 +
Since f is continuous at 0, the limit is finite, so the terms below x3 must vanish: = 0 and = -3
Hence f(0) = - ( 92 - 36 ) = -4
Answer: (3)