SOLUTION: My problem is to find the number c such that the vertex of f(x)=x^2+8x+c lies on the x-axis.

Question 103742This question is from textbook Precalculus A GRAPHING APPROACH
: My problem is to find the number c such that the vertex of f(x)=x^2+8x+c lies on the x-axis. This question is from textbook Precalculus A GRAPHING APPROACH

Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
find the number c such that the vertex of f(x)=x^2+8x+c lies on the x-axis.
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y-c = x^2+8x
Complete the square:
y-c+4^2 = x^2+8x+4^2
(x+4)^2 = y-(c-16)
The vertex is at (-4,c-16)
If the vertex is going to be on the x-axis c-16 must be zero:
c-16 = 0
c = 16
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Cheers,
Stan H.
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