For the function f(x) = x + 3x - 2 (x2 + x ), where x [0, 2 ], consider the following two statements : (I) f is increasing in (0, 2 ). (II) f' is decreasing in (0, 2 ). Between the above two statements,
- only (I) is true.
- both (I) and (II) are true.
- only (II) is true.
- neither (I) nor (II) is true.
Answer
(2) both (I) and (II) are true.
Solution
f'(x) = x + 3 - 2 (2x + 1)
f''(x) = - x - 4 < 0 f' is decreasing (II) is true
least value of f' is f' ( 2 ) = 0 + 3 - 2 - 2 = 1 - 2 > 0
f'(x) > 0 in (0, 2 ) f is increasing (I) is true
Answer: (2)