  ### Home > APCALC > Chapter 7 > Lesson 7.1.5 > Problem7-50

7-50.

Use the first and second derivatives to determine the following locations for $f(x) = xe^x$.

1. Relative minima and maxima

Remember: Finding where $f^\prime(x)= 0$ or $f^\prime(x) =$ DNE will identify CANDIDATES for minima and maxima.
You need to complete the 1st or 2nd Derivative Test to confirm which is which.

2. Intervals over which $f$ is increasing and decreasing

When $f^\prime(x)$ is positive, then $f(x)$ has positive slopes, which means $f(x)$ is increasing.

3. Inflection points

Remember: Finding where $f^{\prime\prime}(x)$ or $f^{''}(x)=$ DNE will identify CANDIDATES for inflection points.
You need to do further investigation to determine if it is (or is not) an inflection point.

Either test for a sign change of $f^{\prime\prime}(x)$ before and after the candidate point. Or evaluate $f^{\prime\prime\prime}$ at the candidate.
If $f^{\prime\prime\prime}(\text{candidate})≠ 0$ , then it is a point of inflection.

4. Intervals over which $f$ is concave up and concave down

When $f^{\prime\prime}(x)$ is positive, then $f^\prime(x)$ has positive slopes, which means $f(x)$ is concave up.