If the domain of the function f(x)= (0.6) ( | 2x-5x2-4 | ) is (- , a] \b\ [c, d) (e, ), then the value of a+b+c+d+e is .
Answer
4
Solution
f is defined when (0.6) | 2x - 5x2 - 4 | 0.
∵ The base 0.6 < 1, this needs 0 < | 2x - 5x2 - 4 | 1, with x 2 and x 52, so
|2x - 5| |x2 - 4|
(x2 - 4)2 - (2x - 5)2 0
(x2 - 2x + 1)(x2 + 2x - 9) 0
(x - 1)2(x2 + 2x - 9) 0
x = 1 or x -1 - 10 or x -1 + 10
Here x = 2 are not in this set, but -1 + 10 2.16 < 52, so x = 52 must be removed. Hence
Domain = (- , -1 - 10 ] \1\ [-1 + 10, 52 ) ( 52, )
so a = -1 - 10, b = 1, c = -1 + 10 and d = e = 52.
∴ a + b + c + d + e = -1 + 1 - 1 + 5 = 4
Answer: 4