Let f(x)= 0x2 t2-8t+15et dt, x . Then the numbers of local maximum and local minimum points of f, respectively, are :
- 3 and 2
- 2 and 2
- 2 and 3
- 1 and 3
Answer
(3) 2 and 3
Solution
f'(x)= x4-8x2+15ex2 2x= 2x(x2-3)(x2-5)ex2
Sign of f' = sign of x(x2-3)(x2-5): five simple roots, + for x> 5, signs alternate (wavy curve)
[figure]
f' changes - + at - 5, 0, 5 (minima) and + - at 3 (maxima)
2 maxima and 3 minima
Answer: (3)