Let e 4 dx ex - 1 = 6. Then e and e- are the roots of the equation :
- 2x2 - 5x + 2 = 0
- x2 - 2x - 8 = 0
- 2x2 - 5x - 2 = 0
- x2 + 2x - 8 = 0
Answer
(1) 2x2 - 5x + 2 = 0
Solution
Put ex - 1 = t2 exdx = 2t dt dx = 2t dt1 + t2
dx ex - 1 = 2 dt1 + t2 = 2 -1t
Limits: t = 3 at x = e 4 and t = e - 1 at x =
2 ( 3 - -1 e - 1 ) = 6 -1 e - 1 = 4
e = 2, e- = 12: sum = 52, product = 1
x2 - 52x + 1 = 0 2x2 - 5x + 2 = 0
Answer: (1)