Expert: Paul Klarreich - 3/18/2010

Question
The line x + y = k, where k is a constant, is tangent to the graph of y = x^2 + 3x + 1.  
Find the value of K.

Answer
Questioner: steve
Country: United States
Category: Calculus
Private: Yes  <<<<< fixed.
Subject: tangent lines and normal lines
Question: The line x + y = k, where k is a constant, is tangent to the graph of y = x^2 + 3x + 1.  
Find the value of K.
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x + y = k  is a line with slope = -1.

Now find:

m = dy/dx = 2x + 3.

Set that = -1 and solve for x.

Then find the y = f(x) for that and you have a point on your line.

You can handle the rest.