Question

Find the values of x where the extreme values of the function y=(x^3)-7x-5x occur.
A. x=-0.33, x=5
B. x=0.33, x=-5
C. x=0.33, x=5
D. x=2, x=5
E. x=0.65, x=7.65
show me how you got the answer Please

Answer 1

is that function right?

Answer 2

Yes

Answer 3

okay well then we can simplify it first by collecting like term:

y=(x^3)-7x-5x
y=x^3-12x
then we find the derivative
y'=3x^2-12
next we set the derivative to zero: 3x^2-12=0-->3(x^2-4)=0-->3(x-2)(x+2)=0
Thus our critical number are:

x-2=0--->x=2 and

x+2=0--->x=-2

Which is of course makes no sense since this not one of your possible choices

Answer 4

maybe we shouldn't combine like terms in the beginning
.

Answer 5

even if you dont we will still get the same answer:

y=x^3-7x-5x
y'=3x^2-7-5
=3x^2-12, see same thing

Answer 6

i suggest you check if that is the correct function

Answer 7

\[y=x^3-7x-5x\]

Answer 8

I'm not lying to you, this function is never gonna have extreme point on one of the choices you posted: http://www.wolframalpha.com/input/?i=y%3Dx%5E3-7x-5x

Answer 9

by extreme points you mean critical points right? max and min

Answer 10

yes