If e y = 3 -1x, then (1 - x2)y'' - xy' at x = 12 is equal to
- 9e /2
- 9e /6
- 3e /2
- 3e /6
Answer
(1) 9e /2
Solution
y = e3 -1x, so y' = 3y 1 - x2, i.e. 1 - x2 y' = 3y
Differentiating again: 1 - x2 y'' - x 1 - x2 y' = 3y'
Multiplying by 1 - x2: (1 - x2)y'' - xy' = 3 1 - x2 y' = 9y
At x = 12, y = e3 /6 = e /2, so the value = 9e /2
Answer: (1)