SOLUTION: Hello, 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

Algebra ->  Rational-functions -> SOLUTION: Hello, 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      Log On


   



Question 1121490: Hello,
Given the following how would I solve for c?
The line function y=2x%2B4 is tangent to the function y=x%5E2%2B8x%2Bc
(I know the answer is: 13 but not sure how to do it)
Thanks

Found 2 solutions by josgarithmetic, muffin8:
Answer by josgarithmetic(39616) About Me  (Show Source):
You can put this solution on YOUR website!
-------------------------------------------------------------------------
Given the following how would I solve for c?
The line function y=2x%2B4 is tangent to the function y=x%5E2%2B8x%2Bc
(I know the answer is: 13 but not sure how to do it)
----------------------------------------------------------------------------

Line touches parabolic function at one single point.
-%28x%5E2%2B8x%2Bc%29%2B%282x%2B4%29=0
-
-x%5E2-8x-c%2B2x%2B4=0
-x%5E2-6x%2B4-c=0
x%5E2%2B6x%2Bc-4=0
x%5E2%2B6x%2B%28c-4%29=0-------discriminant must be 0. ONE solution.


6%5E2-4%2A1%2A%28c-4%29=0
36-4c%2B16=0
-4c=-36-16
4c=36%2B16
c=9%2B4
highlight%28c=13%29


graph%28400%2C400%2C-8%2C4%2C-8%2C4%2Cx%5E2%2B8x%2B13%2C2x%2B4%29

Answer by muffin8(5) About Me  (Show Source):