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Finding equation of both lines

  • Thread starter Meeker
  • Start date
  • #1
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Homework Statement



Determine the equation of both lines that are tangent to the graph of y=x^2 +4 and pass through the point (1,-2)

Homework Equations





The Attempt at a Solution



The derivative/slope of the tangent is 2x. But I'm not too sure what to do with this.
 

Answers and Replies

  • #2
Dick
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Ok so let (x,y) be a point on your curve. That makes it (x,x^2+4), right? Now find the slope of the line between that point and (1,-2). That slope should be your 2x, also right? Now solve for x.
 
  • #3
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Ok so let (x,y) be a point on your curve. That makes it (x,x^2+4), right? Now find the slope of the line between that point and (1,-2). That slope should be your 2x, also right? Now solve for x.
Alright. Once I find x, what do I do with it?.

Btw, the slope for that line is (x-1)/(x^2+6) rite?
 
  • #4
Dick
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Alright. Once I find x, what do I do with it?.

Btw, the slope for that line is (x-1)/(x^2+6) rite?
Slope is delta(y)/delta(x), isn't it? Once you find values for x, each one gives you a point on the curve that also goes through (1,-2). Use the points to find the line equations.
 

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