Question
The function 2x3 – 9x2 + 12x – 3 is increasing when x belongs to the interval
- (-, 2) È (2, )
- (-, 1) È (2, )
- (-, 3) È (3, )
- None
Hint:
We are given a function. We have to find the interval in which the function is increasing.
The correct answer is: (-, 1) È (2, )
The given function is
To find the extremum value, we will take the derivate of the function and equate it to zero
Point 2 and 1 can be minima or maxima
To find the interval, we will consider two cases
1 points greater that 2
2) points less than 1
We will substitute any arbitrary value of the interval in first derivative and see if the function is increasing or decreasing.
fIf first derivative is positive the given function is increasing and if first derivative is negative the given function is decreasing.
Case 1) x > 2
We will take x = 4
f'(4) = 6(4 - 2)(4 - 1)
= 36
Hence, above 2 the value is increasing.
Case 2) x< 1
We will take x = 0
f'(0) = 6(0 - 2)(0 - 1)
= 12
Hence, the below 0 the value of the function is increasing.
So, the interval will be (-∞, 1)È(2,∞)
We should know the way to find the minimum or maximum value.
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