Help with Algebra 2/Trigonometry problem

  • Thread starter daodude1987
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  • #1
daodude1987

Main Question or Discussion Point

I'm having trouble with proving this equation: x=-b\2a
I am not really familiar with this equation but my trigonometry teacher says it is something from Algebra 2. How can I prove why or how this equation works for finding the x-coordinate?
 

Answers and Replies

  • #2
HallsofIvy
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What do you mean "prove it"? It's an equation- its sometimes true and sometimes not. I suppose you mean "prove it is true for this particular situation" but you haven't told us what the situation is.
Could you please state the entire problem exactly?
 
  • #3
Using simple calculus, you can show that x=-b/2a is the point at which a parabola attains a minimum or maximum.
The vertical line x=-b/2a that goes thru this point is the axis of symmetry.
 
  • #4
HallsofIvy
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Ah! Thanks, Stephen, I recognized "-b/(2a)" as part of the quadratic formula but didn't recognize that he was asking for a proof that the x coordinate of the vertex of the parabola y= ax2+ bx+ c is -b/(2a).
 
  • #5
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wait isn't -b/2a the vertex of a parabola? i kinda of forgot this but i think you can the coeficients of b and a get the vertex of the parabola
 
  • #6
HallsofIvy
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Yes, that was what StephenPrivitera told you!
 
  • #7
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o sorry i only saw the oroginal question
 

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