If 2 3 x+ 2x x+4 x-4=0 has exactly 3 solutions in the interval [0, n 2 ], n N, then the roots of the equation x2+nx+(n-3)=0 belong to :
- (0, )
- Z
- (- 172, 172 )
- (- , 0)
Answer
(4) (- , 0)
Solution
2x x=2 x 2x
2 x ( 2x+ 2x )+4 x-4=0 x= 23
Solutions: , - , 2 + , 3 - , where = -1 23< 2
exactly 3 of them lie in [0, n 2 ] only when 2 + n 2<3 - n=5
x2+5x+2=0 x= -5 172
17<5, both roots are negative roots (- , 0)
Answer: (4)