Question

f(x) = x e^(-x).
find concave up or down

Answer 1

Use what we told you. Find the critical numbers. Use the Second Derivative Test to find concavity.

Answer 2

second derivative is (e^(-x)) (-2+x)
whats next , how i find the numbers

Answer 3

Hmm, from what I know, you find the critical numbers by setting the first derivative equal to 0.

Answer 4

Solve for x. Then use the SDT.

Answer 5

ok so first i find critical numbers ?

Answer 6

That;s what I would do. Anyone else got another strategy, that doesn't involve graphing? lol

Answer 7

-e^(-x) (-1+x) = 0

Answer 8

cant find critical numbers with this eq

Answer 9

is critical number 1 ?

Answer 10

Yes lol. That would be the only one since an exponential function cannot equal 0.