in Linear Algebra edited by
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The minimum value of the function $f(x)=x^3/3-x$  occurs at 

  1. x= 1
  2. x= -1
  3. x= 0
  4. x= $\frac{1}{\sqrt[]{3}}$
in Linear Algebra edited by
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given f(x) = x/3 - x

for maxima and minima

f '(x) = 0

so f '(x) = x- 1 = 0

ie x = 1,-1

f ''(x) = 2x

here 

f ''(1) = 2 >0 (positive)

f ''(-1) = -2 <0 (negative)

we know if f ''(a) >0 then will be minima at x=a

and if f ''(a) <0 then will be maxima at x=a

so here at x=1 f(x) has minimum value

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