`f(x) = x^4 - 2x^2 + 3` (a) Find the intervals on which `f` is increasing or decreasing. (b) Find the local maximum and minimum values of `f`. (c) Find the intervals of concavity and the inflection points.
- print Print
- list Cite
Expert Answers
calendarEducator since 2012
write1,284 answers
starTop subjects are Math and Science
`f(x) =x^4 - 2x^2 + 3`
(a) To solve, take the derivative of the given function.
`f'(x) =4x^3 - 4x`
Then, set the derivative equal to zero.
`0=4x^3-4x`
Factor the right side of the equation.
`0=4x(x^2-1)`
`0=4x(x-1)(x+1)`
Set each factor equal to zero. And isolate the x in each equation.
Factor 1:
`4x=0`
`x=0`
Factor 2:
`x-1=0`
`x=1`
Factor 3:
`x + 1 =0`
`x=-1`
So, f(x) has three critical numbers. These are x=-1, x=0 and x=1. The intervals formed by these three critical numbers are:
`(-oo, -1)` `(-1,0)` `(0,1)` and `(1,oo)` .
To determine which among the intervals is the function increasing or decreasing, assign a test value for each. Plug-in the test value to the derivative
`f'(x) = 4x^3-4x.`
If the result of f'(x) is negative, the function is decreasing in that interval. And if the result is positive, the function is increasing in that interval.
For the first interval (-inf,-1), let the test value be x=-2.
`f'(-2) = 4(-2)^3 - 4(-2)=-24 ` (Decreasing)
For the second interval...
(The entire section contains 650 words.)
Unlock This Answer Now
Start your 48-hour free trial to unlock this answer and thousands more. Enjoy eNotes ad-free and cancel anytime.
Related Questions
- `f(x) = (x^2) - x - ln(x)` (a) Find the intervals on which `f` is increasing or decreasing....
- 2 Educator Answers
- `f(x) = x/(x^2 + 1)` (a) Find the intervals on which `f` is increasing or decreasing. (b)...
- 1 Educator Answer
- `f(x) = (x^2)ln(x)` (a) Find the intervals on which `f` is increasing or decreasing. (b)...
- 1 Educator Answer
- `f(x) = e^(2x) + e^(-x)` (a) Find the intervals on which `f` is increasing or decreasing....
- 1 Educator Answer
- `f(x) = 2x^3 + 3x^2 - 36x` (a) Find the intervals on which `f` is increasing or decreasing....
- 1 Educator Answer
`f'(x) = 4x^3 - 4x `
Let's find where `f'(x) = 0` :
`4x^3 - 4x = 0 `
`x = 0 or x = -1 or x = 1 `
If `x lt -1` , then `f'(x) lt 0` . For example, if `x = -2` , then `f'(x) = -24` . Therefore, the function is decreasing in that region.
If `-1 lt x lt 0` , then `f'(x) gt 0` . For example, if `x = -(1/2)` , then `f'(x) = 3/2` . Therefore, the function is increasing in that region.
If `0 lt x lt 1` , then `f'(x) lt 0` . For example, if `x = 1/2` , then `f'(x) = -3/2` . Therefore, the function is decreasing in that region.
If `x gt 1` , then `f'(x) gt 0` . For example, if `x = 2` , then `f'(x) = 24` . Therefore, the function is increasing in that region.
So the answer is: `f(x)` is increasing where `-1 lt x lt 0` and where `x gt 1`
`f''(x)=12x^2 - 4` and `f''(x)=0` when x = `+-1/3` .
So, f is concave up as x belongs to `(-oo,-1/3)` or `(1/3,oo) `
and f is concave down as x belongs to `(-1/3,1/3)` .
Student Answers