Trying to figure out how to get correct vertex on parabola question.

label Algebra
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-1/2 x^2 + 5x -8

I understand that I have to divide 5, and square it, and all that but I never end up with the correct vertex of 5,9/2 I only come up with 5,7/4

Oct 6th, 2015

Thank you for the opportunity to help you with your question!

(-1/2)*x^2 + 5x -8

x-coordinate of the vertex: -b/2a=-5/2*(-1/2)=-5/(-1)=5

y-coordinate of the vertex: (-1/2)*5^2 + 5*5 -8=-25/2+25-8=(-25+50-16)/2=9/2

so vertex is (5, 9/2)

Please let me know if you need any clarification. I'm always happy to answer your questions.
Oct 6th, 2015

I think I understand, it isn't the same method my teacher uses, but it at least gets the job done. Thank you!

Oct 6th, 2015

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