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CalculusMultivariable CalculusIf a function of one variable is continuous on an interval and has only one critical number, then a local maximum has to be an absolute maximum. But this is not true for functions of two variables. Show that the function f( x , y ) = 3 xe y − x 3 − e 3 y has exactly one critical point, and that f has a local maximum there that is not an absolute maximum. Then use a computer to produce a graph with a carefully chosen domain and view-point to see how this is possible.BuyFind*arrow_forward*

8th Edition

James Stewart

Publisher: Cengage Learning

ISBN: 9781305266643

Chapter 14.7, Problem 40E

Textbook Problem

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If a function of one variable is continuous on an interval and has only one critical number, then a local maximum has to be an absolute maximum. But this is not true for functions of two variables. Show that the function

f(*x*, *y*) = 3*xe ^{y}* −

has exactly one critical point, and that *f* has a local maximum there that is not an absolute maximum. Then use a computer to produce a graph with a carefully chosen domain and view-point to see how this is possible.

Expert Solution

To determine

**To show:** The function
*f* has a local maximum there that is not an absolute maximum and use a computer graph to view the point.

**Result used:**

**Second Derivative Test:**

“Suppose the second partial derivatives of *f* are continuous on a disk with center
*f*).

Let

**Given:**

The function is,

**Calculation:**

Take the partial derivative in the given function with respect to *x* and obtain

Thus,

Take the partial derivative in the given function with respect to *y* and obtain

Thus,

Set the above partial derivatives to 0 and find the values of *x* and *y*.

From the equation (1),

Substitute

If

Substitute

Thus, the critical point is

Multivariable Calculus

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(a) Show that a differentiable function f...Ch. 14.6 - Find the directions in which the directional...Ch. 14.6 - Find all points at which the direction of fastest...Ch. 14.6 - Near a buoy, the depth of a lake at the point with...Ch. 14.6 - The temperature T in a metal ball is inversely...Ch. 14.6 - The temperature at a point (x, y, z) is given by...Ch. 14.6 - Suppose that over a certain region of space the...Ch. 14.6 - Suppose you are climbing a hill whose shape is...Ch. 14.6 - Let f be a function of two variables that has...Ch. 14.6 - Shown is a topographic map of Blue River Pine...Ch. 14.6 - Show that the operation of taking the gradient of...Ch. 14.6 - Sketch the gradient vector f(4. 6) for the...Ch. 14.6 - The second directional derivative of f(x, y) is...Ch. 14.6 - (a) If u = a, b is a unit vector and f has...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Find equations of (a) the tangent plane and (b)...Ch. 14.6 - Use a computer to graph the surface, the tangent...Ch. 14.6 - Use a computer to graph the surface, the tangent...Ch. 14.6 - If f(x, y) = xy, find the gradient vector f(3, 2)...Ch. 14.6 - If g(x, y) = x2 + y2 4x, find the gradient vector...Ch. 14.6 - Show that the equation of the tangent plane to the...Ch. 14.6 - Find the equation of the tangent plane to the...Ch. 14.6 - Show that the equation of the tangent plane to the...Ch. 14.6 - At what point on the ellipsoid x2 + y2 + 2z2 = 1...Ch. 14.6 - Are there any points on the hyperboloid x2 y2 z2...Ch. 14.6 - Show that the ellipsoid 3x2 + 2y2 + z2 = 9 and the...Ch. 14.6 - Show that every plane that is tangent to the cone...Ch. 14.6 - Show that every normal line to the sphere x2 + y2...Ch. 14.6 - Where does the normal line to the paraboloid z =...Ch. 14.6 - At what points does the normal line through the...Ch. 14.6 - Show that the sum of the x-, y-, and z-intercepts...Ch. 14.6 - Show that the pyramids cut off from the first...Ch. 14.6 - Find parametric equations tor the tangent line to...Ch. 14.6 - (a) The plane y + z = 3 intersects the cylinder x2...Ch. 14.6 - Where does the helix r(t) = cos t, sin t, t...Ch. 14.6 - The helix r(t) = cos(t/2), sin(t/2), t) intersects...Ch. 14.6 - (a) Two surfaces are called orthogonal at a point...Ch. 14.6 - (a) Show that the function f(x, y) = xy3 is...Ch. 14.6 - Suppose that the directional derivatives of f(x,...Ch. 14.6 - Show that if z = f(x, y) is differentiable at x0 =...Ch. 14.7 - Suppose (1, 1) is a critical point of a function f...Ch. 14.7 - Suppose (0, 2) is a critical point of a function y...Ch. 14.7 - Use the level curves in the figure to predict the...Ch. 14.7 - Use the level curves in the figure to predict the...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Find the local maximum and minimum values and...Ch. 14.7 - Show that f(x, y) = x2 + 4y2 4xy + 2 has an...Ch. 14.7 - Show that f(x,y)=x2yex2y2 has maximum values at...Ch. 14.7 - Use a graph or level curves or both to estimate...Ch. 14.7 - Use a graph or level curves or both to estimate...Ch. 14.7 - Use a graph or level curves or both to estimate...Ch. 14.7 - Use a graph or level curves or both to estimate...Ch. 14.7 - Use a graphing device as in Example 4 (or Newtons...Ch. 14.7 - Use a graphing device as in Example 4 (or Newtons...Ch. 14.7 - Use a graphing device as in Example 4 (or Newtons...Ch. 14.7 - Use a graphing device as in Example 4 (or Newtons...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - Find the absolute maximum and minimum values of f...Ch. 14.7 - For functions of one variable it is impossible for...Ch. 14.7 - If a function of one variable is continuous on an...Ch. 14.7 - Find the shortest distance from the |point (2, 0,...Ch. 14.7 - Find the point on the plane x 2y + 3z = 6 that is...Ch. 14.7 - Find the points on the cone z2 = x2 + y2 that are...Ch. 14.7 - Find the points on the surface y2 = 9 + xz that...Ch. 14.7 - Find three positive numbers whose sum is 100 and...Ch. 14.7 - Find three positive numbers whose sum is 12 and...Ch. 14.7 - Find the maximum volume of a rectangular box that...Ch. 14.7 - Find the dimensions of the box with volume 1000...Ch. 14.7 - Find the volume of the largest rectangular box in...Ch. 14.7 - Find the dimensions of the rectangular box with...Ch. 14.7 - Find the dimensions of a rectangular box of...Ch. 14.7 - The base of an aquarium with given volume V is...Ch. 14.7 - A cardboard box without a lid is to have a volume...Ch. 14.7 - A rectangular building is being designed to...Ch. 14.7 - If the length of the diagonal of a rectangular box...Ch. 14.7 - A model for the yield Y of an agricultural crop as...Ch. 14.7 - The Shannon index (sometimes called the...Ch. 14.7 - Three alleles (alternative versions of a gene) A,...Ch. 14.7 - Suppose that a scientist has reason to believe...Ch. 14.7 - Find an equation of the plane that passes through...Ch. 14.8 - Pictured are a contour map of f and a curve with...Ch. 14.8 - (a) Use a graphing calculator or computer to graph...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - Each of these extreme value problems has a...Ch. 14.8 - The method of Lagrange multipliers assumes that...Ch. 14.8 - Find the minimum value of f(x, y, z) = x2 + 2y2 +...Ch. 14.8 - Find the extreme values of f subject to both...Ch. 14.8 - Find the extreme values of f subject to both...Ch. 14.8 - Find the extreme values of f subject to both...Ch. 14.8 - Find the extreme values of f subject to both...Ch. 14.8 - Find the extreme values of f on the region...Ch. 14.8 - Find the extreme values of f on the region...Ch. 14.8 - Find the extreme values of f on the region...Ch. 14.8 - Consider the problem of maximizing the function...Ch. 14.8 - Consider the problem of minimizing the function...Ch. 14.8 - The total production P of a certain product...Ch. 14.8 - Referring to Exercise 27, we now suppose that the...Ch. 14.8 - Use Lagrange multipliers to prove that the...Ch. 14.8 - Use Lagrange multipliers to prove that the...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Use Lagrange multipliers to give an alternate...Ch. 14.8 - Find the maximum and minimum volumes of a...Ch. 14.8 - The plane x + y + 2z = 2 intersects the paraboloid...Ch. 14.8 - The plane 4x 3y + 8z = 5 intersects the cone z2 =...Ch. 14.8 - (a) Find the maximum value of...Ch. 14.8 - (a) Maximize i=1nxiyi subject to the constraints...Ch. 14 - (a) What is a function of two variables? (b)...Ch. 14 - What is a function of three variables? How can you...Ch. 14 - What does lim(x,y)(a,b)f(x,y)=L mean? How can you...Ch. 14 - (a) What does it mean to say that f is continuous...Ch. 14 - (a) Write expressions for the partial derivatives...Ch. 14 - What does Clairauts Theorem say?Ch. 14 - How do you find a tangent plane to each of the...Ch. 14 - Define the linearization of f at (a, b). What is...Ch. 14 - (a) What does it mean to say that f is...Ch. 14 - If z = f(x, y), what arc the differentials dx, dy,...Ch. 14 - State the Chain Rule for the case where z = f(x,...Ch. 14 - If z is defined implicitly as a function of x and...Ch. 14 - (a) Write an expression as a limit for the...Ch. 14 - (a) Define the gradient vector f for a function f...Ch. 14 - What do the following statements mean? (a) f has a...Ch. 14 - (a) If f has a local maximum at (a, b), what can...Ch. 14 - State the Second Derivatives Test.Ch. 14 - (a) What is a closed set in 2? What is a bounded...Ch. 14 - Explain how the method of Lagrange multipliers...Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Determine whether the statement is true or false....Ch. 14 - Find and sketch the domain of the function. 1....Ch. 14 - Find and sketch the domain of the function. 2....Ch. 14 - Sketch the graph of the function. 3. f(x, y) = 1 ...Ch. 14 - Sketch the graph of the function. 4. f(x, y) = x2...Ch. 14 - Sketch several level curves of the function. 5....Ch. 14 - Sketch several level curves of the function. 6....Ch. 14 - Make a rough sketch of a contour map for the...Ch. 14 - The contour map of a function f is shown, (a)...Ch. 14 - Evaluate the limit or show that it does not exist....Ch. 14 - Evaluate the limit or show that it does not exist....Ch. 14 - A metal plate is situated in the xy-plane and...Ch. 14 - Find a linear approximation to the temperature...Ch. 14 - Find the first partial derivatives. 13. f(x, y) =...Ch. 14 - Find the first partial derivatives. 14....Ch. 14 - Find the first partial derivatives. 15. F(, ) = 2...Ch. 14 - Find the first partial derivatives. 16. G(x, y, z)...Ch. 14 - Find the first partial derivatives. 17....Ch. 14 - The speed of sound traveling through ocean water...Ch. 14 - Find all second partial derivatives of f. 19. f(x,...Ch. 14 - Find all second partial derivatives of f. 20. z =...Ch. 14 - Find all second partial derivatives of f. 21. f(x,...Ch. 14 - Find all second partial derivatives of f. 22. v =...Ch. 14 - If z = xy + xey/x show that xzx+yzy=xy+z.Ch. 14 - If z = sin(x + sin t), show that zx2zxt=zt2zx2Ch. 14 - Find equations of (a) the tangent plane and (b)...Ch. 14 - Find equations of (a) the tangent plane and (b)...Ch. 14 - Find equations of (a) the tangent plane and (b)...Ch. 14 - Find equations of (a) the tangent plane and (b)...Ch. 14 - Find equations of (a) the tangent plane and (b)...Ch. 14 - Use a computer to graph the surface z = x2 + y4...Ch. 14 - Find the points on the hyperboloid x2 + 4y2 z2 =...Ch. 14 - Find du if u = ln(1 + se2t).Ch. 14 - Find the linear approximation of the function...Ch. 14 - The two legs of a right triangle are measured as 5...Ch. 14 - If u = x2y3 + z4, where x = p + 3p2, y = pep, and...Ch. 14 - If v = x2sin y + yexy, where x = s + 2t and y =...Ch. 14 - Suppose z = f(x, y), where x = g(s, t), y = h(s,...Ch. 14 - Use a tree diagram to write out the Chain Rule for...Ch. 14 - If z = y + f(x2 y2), where f is differentiable,...Ch. 14 - The length x of a side of a triangle is increasing...Ch. 14 - If z =f(u, v), where u = xy, v = y/x, and f has...Ch. 14 - If cos(xyz) = 1 + .x2y2 + z2, find zx and zy.Ch. 14 - Find the gradient of the function f(x,y,z)=x2eyz2.Ch. 14 - (a) When is the directional derivative of f a...Ch. 14 - Find the directional derivative of f at the given...Ch. 14 - Find the directional derivative of f at the given...Ch. 14 - Find the maximum rate of change of f(x,y)=x2y+y at...Ch. 14 - Find the direction in which f(x, y, z) =...Ch. 14 - The contour map shows wind speed in knots during...Ch. 14 - Find parametric equations of the tangent line at...Ch. 14 - Find the local maximum and minimum values and...Ch. 14 - Find the local maximum and minimum values and...Ch. 14 - Find the local maximum and minimum values and...Ch. 14 - Find the local maximum and minimum values and...Ch. 14 - Find the absolute maximum and minimum values of f...Ch. 14 - Find the absolute maximum and minimum values of f...Ch. 14 - Use a graph or level curves or both to estimate...Ch. 14 - Use a graphing calculator or computer (or Newtons...Ch. 14 - Use Lagrange multipliers to find the maximum and...Ch. 14 - Use Lagrange multipliers to find the maximum and...Ch. 14 - Use Lagrange multipliers to find the maximum and...Ch. 14 - Use Lagrange multipliers to find the maximum and...Ch. 14 - Find the points on the surface xy2z3= 2 that are...Ch. 14 - A package in the shape of a rectangular box can be...Ch. 14 - A pentagon is formed by placing an isosceles...Ch. 14 - A rectangle with length L and width W is cut into...Ch. 14 - Marine biologists have determined that when a...Ch. 14 - A long piece of galvanized sheet metal with width...Ch. 14 - For what values of the number r is the function...Ch. 14 - Suppose f is a differentiable function of one...Ch. 14 - (a) Newton's method for approximating a root of an...Ch. 14 - If the ellipse x2/a2 + y2/b2 = 1 is to enclose the...Ch. 14 - Show that the maximum value of the function...

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