SOLUTION: For the function​ below, find the​ value(s) of x in which f'(x)=0. f(x)=(x^2-2)(x^2-√2) (round to three decimal places as needed.)

Algebra ->  Equations -> SOLUTION: For the function​ below, find the​ value(s) of x in which f'(x)=0. f(x)=(x^2-2)(x^2-√2) (round to three decimal places as needed.)      Log On


   



Question 1195274: For the function​ below, find the​ value(s) of x in which f'(x)=0.
f(x)=(x^2-2)(x^2-√2)
(round to three decimal places as needed.)

Found 2 solutions by math_tutor2020, MathLover1:
Answer by math_tutor2020(3817) About Me  (Show Source):
You can put this solution on YOUR website!

Let
g(x) = x^2 - 2
h(x) = x^2 - sqrt(2)

The derivative of each is
g ' (x) = 2x
h ' (x) = 2x
Both arrive at the same derivative because the constants go to 0 (because they don't have any rate of change to them).

Apply the product rule:
f(x) = (x^2 - 2) * (x^2 - sqrt(2))
f(x) = g(x)*h(x)
f ' (x) = g ' (x)*h(x) + g(x)*h ' (x)
f ' (x) = 2x*(x^2 - sqrt(2)) + (x^2-2)*2x
f ' (x) = 2x*(x^2 - sqrt(2) + x^2-2)
f ' (x) = 2x*(2x^2 - sqrt(2)-2)

Set this equal to zero and solve for x.
f ' (x) = 0
2x*(2x^2 - sqrt(2)-2) = 0
2x = 0 or 2x^2 - sqrt(2)-2 = 0
x = 0 or 2x^2 = sqrt(2)+2
x = 0 or x^2 = 0.5sqrt(2)+1
x = 0 or x = sqrt( 0.5sqrt(2)+1 ) or x = -sqrt( 0.5sqrt(2)+1 )
x = 0 or x = 1.30656 or x = -1.30656
x = 0 or x = 1.307 or x = -1.307


Answers:
x = -1.307, x = 0, and x = 1.307

Answer by MathLover1(20849) About Me  (Show Source):
You can put this solution on YOUR website!



f%28x%29=%28x%5E2-2%29%28x%5E2-sqrt%282%29%29.......expand
f%28x%29+=+x%5E4+-+sqrt%282%29%2Ax%5E2+-+2x%5E2+%2B+2sqrt%282%29

f'%28x%29=4x%5E3+-+2xsqrt%282%29+-+4x ........factor
f'%28x%29+=+2+x+%282+x%5E2+-+sqrt%282%29+-+2%29

now find f'%28x%29=0
2+x+%282+x%5E2+-+sqrt%282%29+-+2%29=0 .......will be true if
2+x+=0
or
%282+x%5E2+-+sqrt%282%29+-+2%29=0

if 2+x+=0 => x=0
if 2x%5E2+-+sqrt%282%29+-+2=0+=> 2+x%5E2+=sqrt%282%29+%2B2 => x%5E2+=sqrt%282%29%2F2+%2B1=> x+=sqrt%28sqrt%282%29%2F2+%2B1%29=1.307 or x+=+-sqrt%28sqrt%282%29%2F2+%2B1%29=-1.307+
so, f'%28x%29=0 for x=0, x=1.307,x=+-1.307