Find the critical points for the function f

Answered question

2022-04-24

Find the critical points for the function f (x) = x sin−1 x on the interval [−1, 1]. Identify the
absolute maximum and absolute minimum values. State the intervals for where the functions is increasing,
decreasing.

Answer & Explanation

star233

star233

Skilled2023-04-29Added 403 answers

To find the critical points of the function f(x)=xsin1(x) on the interval [1,1], we need to find the values of x for which f(x)=0 or f(x) is undefined.
First, let's find the derivative of f(x). We can use the product rule and the chain rule:
f(x)=ddx(xsin1(x))
=sin1(x)+xddx(sin1(x))
=sin1(x)+x11x2
Now we need to find where f(x)=0 or f(x) is undefined. Since sin1(x) is defined only on the interval [1,1], we only need to check the endpoints and the interior points of the interval.
At x=1 and x=1, we have f(x)=sin1(x), which is π2 and π2, respectively. Therefore, f(x) is not equal to zero at either endpoint.
To find the critical points in the interior of the interval, we need to solve the equation f(x)=sin1(x)+x11x2=0. We can rewrite this equation as
sin1(x)=x11x2.
Squaring both sides and simplifying, we get
x2=1x2,
which gives us x=±12. However, we need to check whether these values are in the interval [1,1].
Therefore, the critical points are x=12 and x=12.
To identify the absolute maximum and absolute minimum values, we need to evaluate f(x) at the critical points and the endpoints of the interval.
At the endpoints, we have
f(1)=π4andf(1)=π4.
At the critical points, we have
f(12)=π42andf(12)=π42.
Therefore, the absolute maximum value of f(x) on the interval [1,1] is π4, which occurs at x=1, and the absolute minimum value is π42, which occurs at x=12.
To determine the intervals where the function is increasing or decreasing, we need to examine the sign of f(x) on each interval. Recall that f(x)=sin1(x)+x11x2.
On the interval [1,12), f(x) is negative since sin1(x) is negative and x11x2 is also negative. Therefore, f(x) is decreasing on this interval.
On the interval (12,12), f(x) is positive since sin1(x) is positive and x11x2 is also positive. Therefore, f(x) is increasing on this interval.
On the interval (12,1], f(x) is negative since sin1(x) is positive and x11x2 is negative. Therefore, f(x) is decreasing on this interval.
Therefore, the function f(x)=xsin1(x) is increasing on the interval (12,12) and decreasing on the intervals [1,12) and (12,1].

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