Chapter 2.7, Problem 18E

Question 3. A manufacturer has modeled its yearly production function P (the value of its entire production, in millions of dollars) as a Cobb-Douglas function P(L, K) = 1.47L0.65 0.35 where L is the number of labor hours (in thousands) and K is the invested capital (in millions of dollars). ӘР Ət (a) Express the rate of change of production 07-2 in time, in terms of the rate of change of the labor force and the rate of change of the capital in time. (b) Suppose that when L = 30 and K = 8, the labor force is decreasing at a rate of 2000 labor hours per year and capital is increasing at a rate of 500,000 per year. What is the rate of change of production per year?

17. Consider a mass-spring system that satisfies 2y′′(t) + by′(t) + 50y(t) = 0.Which of the following is/are true?(i) If b = 0, the motion is critically damped with period π/5 .(ii) If b = 12, the motion is underdamped.(iii) If b = 40, the motion is overdamped.A. (ii) and (iii) only B. (ii) only C. (i) and (ii) only D. (i) and (iii) only E. All

20. Find the general solution to the differential equation y(4) − 8y′′ + 16y = 0A. y = c1e^2x + c2e^−2xB. y = c1xe^2x + c2xe^−2xC. y = c1e^2x + c2e^−2x + c3xe^2x + c4xe^−2xD. y = c1xe^2x + c2xe^−2x + c3x^2e^2x + c4x^2e^−2xE. y = c1 cos 2x + c2 sin 2x + c3x cos 2x + c4x sin 2x

9. A 1 kg mass is attached to a spring with constant 13 N/m. The system is immersed in amedium which offers a damping force numerically equal to 6 times the instantaneous velocity.If x is the displacement of the mass from equilibrium, measured in meters,then x′′ + 6x′ + 13x = 0 . Which of the following statements is true?A. x(t) = c1e^−t + c2e^−5t, and the system is underdamped.B. x(t) = c1e^−t + c2e^−5t, and the system is overdamped.C. x(t) = c1e^−3t cos(2t) + c2e^−3t sin(2t), and the system is underdamped.D. x(t) = c1e^−3t cos(2t) + c2e^−3t sin(2t), and the system is overdamped.

Question 2 (A partial differential equation). The diffusion equation де Ət = 82 с მx2 where D is a positive constant, describes the diffusion of heat through a solid, or the concentration of a pollutant at time t at a distance x from the source of the pollution, or the invasion of alien species into a new habitat. Verify that the function c(x, t) -x²/(4Dt) = √4πDt is a solution of the diffusion equation.

13. Let y(x) be the solution to the initial value problem y′′ − 10y′ + 25y = 0, y(0) = 1, y′(0) = 3.Then y(1) = ? A. −e^5 B. 1 C. e^5 D. 4/5 e^5 + 1/5 e^−5 E. e^−5

Question 1 (Implicit differentiation). Use implicit differentiation to find Əz/Əx and Əz/ǝy. (a) x²+2y²+3z² 1 (b) ez = xyz (c) x2. y²+ z² − 2z = 4 (d) yz+xln(y) = z²

4. The general solution of the differential equation y′′ + 2y′ + 5y = 0 isA. c1 + c2x B. c1 cos 2x + c2 sin 2x C. c1e^x cos 2x + c2e^x sin 2xD. c1e^−x cos 2x + c2e^−x sin 2x E. None of these.

3. The general solution of the differential equation y′′ + 2y′ + y = 0 isA. c1e^−x + c2e^−x B. c1e^−x + c2e^x C. c1e^−x + c2xe^−xD. c1 cos x + c2 sin x E. c1e^−x