What are the equations for finding common tangents between two curves?

  • Thread starter labinojha
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In summary, to find the equations of common tangents of y^{2}=4ax and x^{2}=4by, the derivatives of both curves are equated and used in the two point form of the straight line equation. However, the resulting equation may have too many cube roots. To simplify, find the general equation for a line tangent to y^{2}=4ax and x^{2}=4by separately.
  • #1
labinojha
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Homework Statement



Finding the equations of common tangents of [itex]y^{2}[/itex]=4ax and [itex]x^{2}[/itex]=4by

Homework Equations



Equating both curves' derivatives :
[itex]\frac{2a}{y}[/itex]=[itex]\frac{x}{2b}[/itex]

The Attempt at a Solution



Calculated both of the curves' derivatives and equated them .
Used the resulting relation in two point form of straight line equation (y-y1)=m(x-x1) .

Got Stuck now! with too many cuberoots .
 
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  • #2
In your equation: [itex]\displaystyle \frac{2a}{y}=\frac{x}{2b}\,,[/itex] the y is from a point on the first curve, the x from a point on the second curve.

Instead, start by doing the following:

Find the general equation for a line tangent to y2=42x.

The find the general equation for a line tangent to x2=4by.
 
Last edited:

1. What is a common tangent equation?

A common tangent equation is a mathematical equation that represents the tangent line that touches two given curves at the same point. It is used to find the point of intersection between the two curves.

2. How do you find the common tangent equation?

To find the common tangent equation, you need to first find the slopes of the two curves at the point of intersection. Then, use the formula y-y1=m(x-x1) where m is the slope and (x1, y1) is the point of intersection to write the equation in point-slope form. Finally, simplify the equation to get the common tangent equation.

3. Can there be more than one common tangent between two curves?

Yes, there can be more than one common tangent between two curves. This can happen when the two curves are parallel to each other or when they have multiple points of intersection.

4. What is the significance of common tangent equations in real life?

Common tangent equations have various applications in real life, especially in the fields of physics and engineering. They are used to determine the point of contact between two objects, such as a ball rolling on a surface, or in designing curved structures like bridges and roller coasters.

5. Can common tangent equations be used for non-linear curves?

Yes, common tangent equations can be used for non-linear curves. However, the process of finding the equation may be more complex as it involves taking the derivatives of the curves to find their slopes.

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