Find the Tangent Lines of y=x/(x+1) Through (1,2)

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SUMMARY

The discussion focuses on finding the equations of the two tangent lines to the curve defined by y=x/(x+1) that pass through the point (1,2). The approach involves sketching the graph, determining the derivative to find the slope, and using the line equation y=ax+b to establish conditions for intersection. The problem leads to a quadratic equation, where the condition for two equal roots is crucial for identifying the tangent lines. Tools like Winplot are suggested for visualizing the curve and tangent lines.

PREREQUISITES
  • Understanding of calculus, specifically derivatives and tangent lines
  • Familiarity with quadratic equations and their properties
  • Basic knowledge of graphing functions and using graphing software like Winplot
  • Ability to manipulate linear equations in the form y=ax+b
NEXT STEPS
  • Learn how to calculate derivatives of functions to find slopes of tangent lines
  • Study the properties of quadratic equations, focusing on conditions for equal roots
  • Explore graphing techniques using Winplot for visualizing functions and their tangents
  • Investigate the geometric interpretation of tangent lines and their equations
USEFUL FOR

Students studying calculus, mathematics educators, and anyone interested in understanding the geometric properties of curves and tangent lines.

davedave
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Can someone help me with this problem?

Consider the curve defined by y=x/(x+1). (1,2) is a point NOT on the curve.
Find the equations of the two tangent lines to the curve passing through the point
(1,2).
 
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There are some ways to attack this problem but my first instinct is to sketch or print the graph then mark the point (1,2) then take a ruler and carefully draw the tangent lines touching one point on each side of the graph. Then take the derivative around those points and use the formula of a line (y=mx+c) and check to see if the gradients run through the points.

This is perhaps tedious to say the least but I don't know how else to tackle the problem without any more information.

btw winplot should help with this.
 
hihi davedave! :smile:

Write y = ax + b for a typical line.

What is the restriction on a and b for it to pass through (1,2)?

Now find the equation for the points of intersection of that line with y=x/(x+1).

That should be a quadratic equation.

What is the condition for that equation to have two equal roots? :smile:
 

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