Solve x^2+xy+y^2=1: Find Rotation & Angle

In summary, the equation x^2+xy+y^2=1 represents an ellipse, which is a closed curve formed by the intersection of a cone and a plane. To solve for rotation and angle, the Trigonometric Substitution Method can be used, with possible values ranging from 0 to 2π. The Completing the Square method can also be used to solve this equation, and it has various applications in fields such as engineering, physics, and astronomy.
  • #1
stunner5000pt
1,461
2
Consider the equation x^2 + xy + y^2 = 1. Find a rotation so that the equation has no cross term.

here a=b=c=1 right
but how do i find an angle by which to rotate?
the text says the angle is pi/4... i don't know how they got that .. though
 
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  • #2
Start by writing it as a matrix equation:

[tex]x^2+xy+y^2=\vec x^T A \vec x[/tex]
 
  • #3
Once you have the A Galileo is talking about, find its eigenvalues and eigenvectors. The eigenvectors give the directions for the new axes.
 

1. What does the equation x^2+xy+y^2=1 represent?

The equation x^2+xy+y^2=1 represents a conic section known as an ellipse. It is a closed curve that is formed by the intersection of a cone and a plane, and it can have varying lengths and widths.

2. How can this equation be solved to find rotation and angle?

To solve this equation for rotation and angle, we can use the Trigonometric Substitution Method. This involves substituting x = rcosθ and y = rsinθ into the equation, where r is the distance from the origin and θ is the angle of rotation.

3. What are the possible values for rotation and angle in this equation?

The values for rotation and angle in this equation can range from 0 to 2π. This represents a full rotation around the origin, with 0 degrees being the starting point and 2π degrees being the ending point.

4. Can this equation be solved without using trigonometric substitution?

Yes, this equation can also be solved using the Completing the Square method. This involves rearranging the equation to the form (x+a)^2 + (y+b)^2 = c, where a, b, and c are constants. The rotation and angle can then be found using the values of a and b.

5. How can this equation be applied in real-world situations?

The equation x^2+xy+y^2=1 can be applied in various fields such as engineering, physics, and astronomy. In engineering, it can be used to design elliptical structures such as arches and bridges. In physics, it can be used to describe the motion of objects in circular orbits. In astronomy, it can be used to calculate the orbits of planets and other celestial bodies.

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