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Find the geometric location of the points of the process 
x^(2)+2y^(2)+3z^(2)+xy+2xz+4yz=8 where the tangent plane is parallel to the 
xy plane.

Find the geometric location of the points of the process x2+2y2+3z2+xy+2xz+4yz=8x^{2}+2y^{2}+3z^{2}+xy+2xz+4yz=8 where the tangent plane is parallel to the xyxy plane.

Full solution

Q. Find the geometric location of the points of the process x2+2y2+3z2+xy+2xz+4yz=8x^{2}+2y^{2}+3z^{2}+xy+2xz+4yz=8 where the tangent plane is parallel to the xyxy plane.
  1. Identify Equation & Condition: Identify the given equation and the condition for the tangent plane.\newlineThe equation is x2+2y2+3z2+xy+2xz+4yz=8x^2 + 2y^2 + 3z^2 + xy + 2xz + 4yz = 8. The tangent plane must be parallel to the xy-plane, which implies the normal to the tangent plane has no z-component, i.e., fz=0\frac{\partial f}{\partial z} = 0.
  2. Calculate Partial Derivative: Calculate the partial derivative of the equation with respect to z.\newlineDifferentiating x2+2y2+3z2+xy+2xz+4yzx^2 + 2y^2 + 3z^2 + xy + 2xz + 4yz with respect to z gives 6z+2x+4y6z + 2x + 4y.
  3. Set Equal & Solve for z: Set the partial derivative equal to zero to find z in terms of x and y.\newline6z+2x+4y=06z + 2x + 4y = 0 leads to z=13(2x+4y)z = -\frac{1}{3}(2x + 4y).
  4. Substitute z into Equation: Substitute z back into the original equation to find the relationship between x and y.\newlineSubstituting z=13(2x+4y)z = -\frac{1}{3}(2x + 4y) into the original equation, we get:\newlinex2+2y2+3(13(2x+4y))2+xy+2x(13(2x+4y))+4y(13(2x+4y))=8x^2 + 2y^2 + 3\left(-\frac{1}{3}(2x + 4y)\right)^2 + xy + 2x\left(-\frac{1}{3}(2x + 4y)\right) + 4y\left(-\frac{1}{3}(2x + 4y)\right) = 8
  5. Simplify Relationship between x and y: Simplify the equation to find a relationship between x and y.\newlineExpanding and simplifying, we get:\newlinex2+2y2+43(x+2y)223x(2x+4y)43y(2x+4y)=8x^2 + 2y^2 + \frac{4}{3}(x + 2y)^2 - \frac{2}{3}x(2x + 4y) - \frac{4}{3}y(2x + 4y) = 8\newlineThis simplifies to:\newlinex2+2y2+43(x2+4xy+4y2)43x283xy163y2=8x^2 + 2y^2 + \frac{4}{3}(x^2 + 4xy + 4y^2) - \frac{4}{3}x^2 - \frac{8}{3}xy - \frac{16}{3}y^2 = 8

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