Find two points on an ellpise that have horizontal tangent

In summary, the equation 5x^2 - 6xy + 5y^2 = 16 represents an ellipse and the task is to find two points on the ellipse where the tangent is horizontal. To solve this, the derivative of the equation is taken and set equal to 0. This yields a correct solution of x = (3/5)y. However, when substituted back into the original equation, the resulting y value is incorrect. The error likely occurred during the back substitution process.
  • #1
zeion
466
1

Homework Statement



The equation 5x^2 - 6xy + 5y^2 = 16 represents an ellipse.

Determine two points on the ellipse at which the tangent is horizontal.


Homework Equations





The Attempt at a Solution



I find the derivative of the equation:

(-10x + 6y) / (-6x + 10y) = 0 iff -10x + 6y = 0, so x = (3/5)y.
Then I sub x back into original equation and get y, I get y = +/- 1/(sqrt(2)), which is wrong.

What did I do wrong?
 
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  • #2
zeion said:
so x = (3/5)y.

This is correct...

zeion said:
Then I sub x back into original equation and get y, I get y = +/- 1/(sqrt(2)), which is wrong.

What did I do wrong?

Something with the back substitution into the original equation.

ehild
 
  • #3
Got it, thanks.
 

Related to Find two points on an ellpise that have horizontal tangent

1. What is an ellipse?

An ellipse is a geometric shape that resembles a flattened circle. It is defined as the set of all points in a plane whose distances from two fixed points, called foci, add up to a constant value.

2. How do you find two points on an ellipse that have horizontal tangents?

To find two points on an ellipse with horizontal tangents, you can use the derivative of the ellipse equation. The points will be located at the intersection of the ellipse and the horizontal line that is tangent to the ellipse at that point.

3. What is a tangent?

A tangent is a straight line that touches a curve at a single point. It is perpendicular to the curve at that point and represents the instantaneous rate of change of the curve at that point.

4. Why is it important to find points on an ellipse with horizontal tangents?

Finding points on an ellipse with horizontal tangents is important in many real-life applications, such as engineering and physics. It allows us to determine the slope of the curve at that point, which can provide valuable information for designing structures or predicting the behavior of moving objects.

5. Are there any special cases when finding points on an ellipse with horizontal tangents?

Yes, there are two special cases: when the horizontal tangent is located at the center of the ellipse, and when the horizontal tangent is parallel to the major axis of the ellipse. In these cases, the derivative of the ellipse equation will be equal to 0, and the points can be found by substituting this value into the equation.

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