Let S be the set of all ( , ) R R such that x (x2)( e x) ( 1x2 )x ( e(1+x)) =0. Then which of the following is (are) correct?
- (-1,3) S
- (-1,1) S
- (1,-1) S
- (1,-2) S
Answer
(2) (-1,1) S, (3) (1,-1) S
Solution
As x : 1x2 1x2, e(1+x) e x, and (x2) oscillates in [-1,1].
Expression (x2) ( e x) - x-(2+ ).
It tends to 0 iff 2+ >0, or 2+ =0 with - <0.
(A) =-3: x1 grows, no. (B) =-1: x-1 0, yes. (C) =-1: yes. (D) =-2, - =3>0: ( x)3 (x2) does not tend to 0, no.
Answer: (B), (C)