Question 1121490
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Given the following how would I solve for c?
The line function {{{y=2x+4}}} is tangent to the function {{{y=x^2+8x+c}}}

(I know the answer is: 13 but not sure how to do it)
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Line touches parabolic function at one single point.
{{{-(x^2+8x+c)+(2x+4)=0}}}
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{{{-x^2-8x-c+2x+4=0}}}
{{{-x^2-6x+4-c=0}}}
{{{x^2+6x+c-4=0}}}
{{{x^2+6x+(c-4)=0}}}-------discriminant must be 0.  ONE solution.



{{{6^2-4*1*(c-4)=0}}}
{{{36-4c+16=0}}}
{{{-4c=-36-16}}}
{{{4c=36+16}}}
{{{c=9+4}}}
{{{highlight(c=13)}}}



{{{graph(400,400,-8,4,-8,4,x^2+8x+13,2x+4)}}}