Question 204250
How do you complete this function equation f(x)=-2x^2+8x-5. I need to find the vertex h,k , compute h and k and graph the quadratic equation. Plus find the max value of f where it occurs.
I started the equation and found h.
a=-2 b=8 c=-5, so using the ormula -b/2a I got -8/2(-2) which gave me -8/-4 which gave me 2. h=2. Where do I go from here?
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What you found:
-b/2a = 2 
is the "axis of symmetry"
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To find 'k', simply plug 2 back into the equation and solve:
f(x)=-2x^2+8x-5
f(2)=-2(2)^2+8(2)-5
f(x)=-8+16-5
f(x)=3
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So, (h,k) = (2,3) vertex
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To plot, looking at the 'a' coefficient (-2), we KNOW it is a parabola that opens downward.  Use the "vertex" above and find two additional points to plot.  The two additional points could be where the parabola crosses the x-axis:
0=-2x^2+8x-5
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*[invoke quadratic "x", -2, 8, -5 ]