The problem asks us to eliminate the $xy$ term from the given equation $x^2 + xy + y^2 = 6$ by rotating the axes. We then need to express the equation in standard form and finally graph the equation showing the rotated axes.

GeometryConic SectionsEllipseRotation of AxesCoordinate Geometry
2025/5/30

1. Problem Description

The problem asks us to eliminate the xyxy term from the given equation x2+xy+y2=6x^2 + xy + y^2 = 6 by rotating the axes. We then need to express the equation in standard form and finally graph the equation showing the rotated axes.

2. Solution Steps

The general form of a conic section is given by
Ax2+Bxy+Cy2+Dx+Ey+F=0Ax^2 + Bxy + Cy^2 + Dx + Ey + F = 0.
In our case, A=1A = 1, B=1B = 1, C=1C = 1, D=0D = 0, E=0E = 0, and F=6F = -6.
To eliminate the xyxy term, we need to rotate the axes by an angle θ\theta such that
cot(2θ)=ACB\cot(2\theta) = \frac{A - C}{B}.
cot(2θ)=111=0\cot(2\theta) = \frac{1 - 1}{1} = 0
2θ=π22\theta = \frac{\pi}{2}
θ=π4\theta = \frac{\pi}{4}
The rotation equations are:
x=xcosθysinθx = x' \cos\theta - y' \sin\theta
y=xsinθ+ycosθy = x' \sin\theta + y' \cos\theta
Since θ=π4\theta = \frac{\pi}{4}, we have cosθ=sinθ=12\cos\theta = \sin\theta = \frac{1}{\sqrt{2}}.
So, x=12(xy)x = \frac{1}{\sqrt{2}}(x' - y') and y=12(x+y)y = \frac{1}{\sqrt{2}}(x' + y').
Substituting these into the equation x2+xy+y2=6x^2 + xy + y^2 = 6, we get:
(12(xy))2+(12(xy))(12(x+y))+(12(x+y))2=6(\frac{1}{\sqrt{2}}(x' - y'))^2 + (\frac{1}{\sqrt{2}}(x' - y'))(\frac{1}{\sqrt{2}}(x' + y')) + (\frac{1}{\sqrt{2}}(x' + y'))^2 = 6
12(x22xy+y2)+12(x2y2)+12(x2+2xy+y2)=6\frac{1}{2}(x'^2 - 2x'y' + y'^2) + \frac{1}{2}(x'^2 - y'^2) + \frac{1}{2}(x'^2 + 2x'y' + y'^2) = 6
12x2xy+12y2+12x212y2+12x2+xy+12y2=6\frac{1}{2}x'^2 - x'y' + \frac{1}{2}y'^2 + \frac{1}{2}x'^2 - \frac{1}{2}y'^2 + \frac{1}{2}x'^2 + x'y' + \frac{1}{2}y'^2 = 6
32x2+12y2=6\frac{3}{2}x'^2 + \frac{1}{2}y'^2 = 6
Dividing by 6, we get:
x24+y212=1\frac{x'^2}{4} + \frac{y'^2}{12} = 1
This is an ellipse with a2=12a^2 = 12 and b2=4b^2 = 4, so a=12=23a = \sqrt{12} = 2\sqrt{3} and b=2b = 2.

3. Final Answer

The equation in standard form is x24+y212=1\frac{x'^2}{4} + \frac{y'^2}{12} = 1. This is an ellipse centered at the origin, with major axis along the yy'-axis and minor axis along the xx'-axis. The angle of rotation is θ=π4\theta = \frac{\pi}{4}.

Related problems in "Geometry"

The problem asks us to find the projection of vector $\textbf{w}$ onto vector $\textbf{u}$, given $\...

VectorsProjectionDot ProductLinear Algebra
2025/6/2

The problem asks us to find all vectors that are perpendicular to both $v = (1, -2, -3)$ and $w = (-...

VectorsDot ProductOrthogonalityLinear Algebra3D Geometry
2025/6/2

We are given three vectors: $a = (\sqrt{3}/3, \sqrt{3}/3, \sqrt{3}/3)$, $b = (1, -1, 0)$, and $c = (...

VectorsDot ProductAngles3D Geometry
2025/6/2

We are given two problems. Problem 43: An object's position $P$ changes so that its distance from $(...

3D GeometrySpheresPlanesDistance FormulaCompleting the Square
2025/6/2

The problem asks us to find the center and radius of the sphere given by the equation $4x^2 + 4y^2 +...

3D GeometrySphereCompleting the SquareEquation of a Sphere
2025/6/2

The problem asks us to identify the type of curve represented by the polar equation $r = \frac{4}{1 ...

Conic SectionsPolar CoordinatesHyperbolaEccentricity
2025/6/1

The problem asks us to identify the curve represented by the polar equation $r = \frac{-4}{\cos \the...

Polar CoordinatesConic SectionsEccentricityCoordinate Transformation
2025/6/1

We are asked to find the Cartesian equation of the graph of the polar equation $r - 5\cos\theta = 0$...

Polar CoordinatesCartesian CoordinatesCoordinate GeometryCirclesEquation Conversion
2025/6/1

We are given several Cartesian equations and asked to find their corresponding polar equations. Prob...

Coordinate GeometryPolar CoordinatesEquation Conversion
2025/6/1

The problem is to eliminate the cross-product term in the equation $4xy - 3y^2 = 64$ by a suitable r...

Conic SectionsRotation of AxesHyperbolaCoordinate Geometry
2025/6/1