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Point of Inflection Problem

  • #1

Homework Statement


If the graph of y=x^3+ax^2+bx-8 has a point of inflection at (2,0), what is the value of b?
the answer is 8.

Homework Equations





The Attempt at a Solution


y'=3x^2+2ax+b
y''=6x+2a
Let y''=0=6x+2a then i plugged in 2 for x
and got -6=a
So y'=3x^2-12x+b...
I dont know where to go from here.
 

Answers and Replies

  • #2
dx
Homework Helper
Gold Member
2,011
18
You get one more equation from the fact that y = 0 at x = 2.
 
  • #3
i wouldnt of thought of that.
thank you
 

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