Homework Help: math

Posted by Pd on Sunday, July 11, 2010 at 2:17pm.

f(x)=-x^3+3x^2+9x-5

asked to find the stationary points this was my working and i don't know if it is correct

f dash of x = -3x^2+3(2x)+9
-3x^2+6x+9

at local max and min f(x) should =0

-3x^2+6x+9=0
3x^2-6x+9
x^2-2x+3=0

stationary points would be at (x+3) (x-3)
but am i right... if not a nudge in the right direction would be a great help

math - bobpursley, Sunday, July 11, 2010 at 2:53pm
factor x^2-2x+3

(x-3)(x+1)=0
x=3 x=-1

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