Directional Derivatives Quiz

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Questions and Answers

What is the equation of the tangent plane at the point (1, 0, 0) to the surface z = ln(x² + y²)?

  • z = x - y - 1
  • z = x + y - 1
  • z = 2x + y - 1
  • z = x - 1 (correct)

What is the equation of the tangent plane at the point (1, 1, 5) to the graph of f(x, y) = x² + 2xy + 2y²?

  • z = 5x + 3y - 2
  • z = 3x + 2y - 4
  • z = 2x + 4y - 3
  • z = 4x + 6y - 5 (correct)

What is the equation of the tangent plane at the point (x₁, y₁, z₁) to the surface z = √(xy)?

  • y₁x + x₁y - 2z₁z = 0 (correct)
  • y₁x - x₁y + z₁z = 0
  • 2y₁x + x₁y - z₁z = 0
  • x₁y + y₁x - z₁z = 0

What is the equation of the normal line to the surface f(x, y) = x² + y⁴ + e^(xy) at the point (1, 0, 2)?

<p>x = 1 - 2t, y = -t, z = 2 - t (A)</p> Signup and view all the answers

What is the gradient of f at the point P(2, -1) where f(x, y) = x³y + y³x - 2xy?

<p>(-11, -16) (B)</p> Signup and view all the answers

What is the equation of the tangent plane to the surface f(x, y) = x / (x + y) at the point (x₀, y₀) = (1, 1)?

<p>x - y - 4z + 2 = 0 (B)</p> Signup and view all the answers

What is the first derivative of z with respect to t in terms of f, φ, and u?

<p>f'xφ' + f'y*u' (D)</p> Signup and view all the answers

What is the second derivative of z with respect to t in terms of f, φ, and u?

<p>f''x(φ')^2 + 2f''x<em>yphi'<em>u' + f''y(u')^2 + f'x</em>φ'' + f'y</em>u'' (A)</p> Signup and view all the answers

What is the directional derivative of f(x, y) = xy at (x0, y0) in the direction of (h, k) = (1, 1)?

<p>√2 (C)</p> Signup and view all the answers

What is the directional derivative of f(x, y) = 2x + y - 1 at (2, 1) in the direction of (1, 1)?

<p>3√2/2 (D)</p> Signup and view all the answers

What is the directional derivative of g(x, y) = xe^(yx) - xy at (1, 1) in the direction of (3, 4)?

<p>2e - 7/5 (A)</p> Signup and view all the answers

What is the directional derivative of f(x, y) = x + 2x^2 - 3xy at (1, 1) in the direction of (3/5, 4/5)?

<p>-6/5 (A)</p> Signup and view all the answers

What is the partial derivative of 𝑥1 with respect to 𝑝1?

<p>−0.4𝑝1−1.4 𝑒0.2𝑝2 (B)</p> Signup and view all the answers

What is the relationship between 𝑋1 and 𝑋2 based on the given demand functions?

<p>They are substitute goods. (D)</p> Signup and view all the answers

What is the partial derivative of 𝑥2 with respect to 𝑝2?

<p>−0.6𝑝2−1.6 𝑒0.5𝑝1 (A)</p> Signup and view all the answers

What is the formula for the partial price elasticity of demand?

<p>−𝑎11 𝑝2 + 𝑎1 𝑒 (B)</p> Signup and view all the answers

What is the demand function for 𝑥1 in the second scenario?

<p>𝑥1 = 2𝑝1−0.6 𝑝20.8 (B)</p> Signup and view all the answers

What type of goods are 𝑋1 and 𝑋2 in the second scenario?

<p>Substitute goods (C)</p> Signup and view all the answers

What is the condition for a function 𝑓(𝑥, 𝑦) to be homogeneous of degree 𝑟?

<p>𝑓(𝑥, 𝑦) = 𝑥 𝑟 𝜓(𝑦/𝑥) (A)</p> Signup and view all the answers

What is the value of cross-price elasticity of good 1 with respect to the price of good 2?

<p>0.8 (C)</p> Signup and view all the answers

What is the percentage change in the quantity demanded of good 1 when the price of good 1 increases by 2% from the existing level?

<p>1.6% (D)</p> Signup and view all the answers

What is the degree of homogeneity of the function 𝑧 = 𝑥 2 + 2𝑥 2 𝑦 2 + 𝑦 4 /𝑥 + 𝑦?

<p>2 (B)</p> Signup and view all the answers

What is the value of own-price elasticity of good 2?

<p>-0.5 (A)</p> Signup and view all the answers

What is the property of the first partial derivatives of a homogeneous function of degree 𝑟?

<p>They are homogeneous of degree 𝑟 - 1 (B)</p> Signup and view all the answers

What type of goods are good 1 and good 2 based on the given demand functions?

<p>Competitive (C)</p> Signup and view all the answers

What is the Euler's theorem for a homogeneous function of degree 𝑟?

<p>𝑥(𝜕𝑧/𝜕𝑥) + 𝑦(𝜕𝑧/𝜕𝑦) = 𝑟𝑧 (A)</p> Signup and view all the answers

Determine the degree of homogeneity of the function 𝑧 = 2(𝑎𝑥 + 𝑏𝑦)2 - (𝑥 2 + 𝑦 2 )?

<p>2 (C)</p> Signup and view all the answers

What is the value of cross-price elasticity of good 2 with respect to the price of good 1?

<p>0.7 (B)</p> Signup and view all the answers

What is the percentage change in the quantity demanded of good 2 when the price of good 2 decreases by 2% from the existing level?

<p>1.4% (B)</p> Signup and view all the answers

What is the condition for a function 𝑓(𝑥, 𝑦) to be homogeneous of degree 0?

<p>𝑓(𝑥, 𝑦) = 𝜓(𝑦/𝑥) (C)</p> Signup and view all the answers

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