Question

suppose f(x)= x^4 +ax^2. What is the value of a if f has a local min at x=2?

Answer 1

suppose . [f(x)=x^{4}+ax ^{2.}\] What is the value of a if f has a local min at x=2?

Answer 2

im not sure if im supposed to find the derivative then set x = 2 then solve for a
or something else..

Answer 3

If there is a local min at x=2, then f'(2)=0.

Answer 4

If it has a local min, then we know the derivative at that point must be 0. So take the derivative, set x = 2, and set the derivative =0, then solve for a.

Answer 5

Which is essentially what Xavier said, but with more words ;p

Answer 6

okay, i did that.. the answer is -8 but i got -4

Answer 7

Did you get
4x^3+2ax=0 as the derivative?

Answer 8

yes

Answer 9

Substitute x=2
4(2)^2+4a=0

Answer 10

4(2)^3+4a=0 I mean

Answer 11

it would be 4(2)^3

Answer 12

yeah

Answer 13

4a=-32

Answer 14

ohhh. okay.
wow.

Answer 15

thank soo much. im stupid..

Answer 16

Everyone has those moments :P

Answer 17

tag!!

Answer 18

tag