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Worksheets

Partial Derivatives

Total questions: 10

Worksheet time: 15mins

Name
Class
Date
1.

Find the first order partial derivative with respect to y
 f(x,y)=x3y2+3xeyf(x,y)=x^3y^2+3xe^y  
.

a)

 fy(x,y)=3x2y2+3eyf_y(x,y)=3x^2y^2+3e^y  

b)

 fy(x,y)=3x2y2+2x3y+3ey+3xeyf_y(x,y)=3x^2y^2+2x^3y+3e^y+3xe^y  

c)

 fy(x,y)=2x3y+3xeyf_y(x,y)=2x^3y+3xe^y  

d)

 fy(x,y)=6x2+3eyf_y(x,y)=6x^2+3e^y  

2.

The temperature at T at a location in the Northern Hemisphere depends on longitude x, latitude y, and time t, so we can write T=f(x,y,t). The time measured since January 1. What is the meaning of the partial derivatives dT/dx?

a)

The rate of change of temperature with respect to time

b)

The rate of change of temperature as longitude and time varies

c)

The rate of change of temperature as longitude varies with latitude and time fixed

d)

The rate of change of the time with respect to temperature

3.

Find dy/dx by Implicit Differentiation
 2xy3x2y=22xy^3-x^2y=2  

a)

 2xy2y32xy-2y^3  

b)

 2y(xy2)x(6y2x)\frac{2y\left(x-y^2\right)}{x\left(6y^2-x\right)}  

c)

 2yx\frac{-2y}{x}  

d)

 22  

4.

Suppose at the point (1,2, f(1,2)),  fxx(1,2)=5f_{xx}\left(1,2\right)=-5  , fyy(1,2)=4f_{yy}\left(1,2\right)=4  , and  fxy(1,2)=2f_{xy}\left(1,2\right)=-2  .  Then at that point there is a:  

a)

Saddle point

b)

Local Max

c)

Local Min

d)

Cannot be determined

5.

When finding local extrema, suppose the D>0 and  at a point.  Then that point is: 

a)

A local max

b)

A local min

c)

A saddle point

d)

Cannot be determined.

6.

Use implicit differentiation to find  zx\frac{\partial z}{\partial x}  given that  yz4+x2z3=exyzyz^4+x^2z^3=e^{xyz}  .

a)

 yzexyz2xz34yz3+3x2z2xyexyz\frac{yze^{xyz}-2xz^3}{4yz^3+3x^2z^2-xye^{xyz}}  

b)

 2xz3yzexyz4yz3+3x2z2xyexyz\frac{2xz^3-yze^{xyz}}{4yz^3+3x^2z^2-xye^{xyz}}  

c)

 4yz3+3x2z2xyexyzyzexyz2xz3\frac{4yz^3+3x^2z^2-xye^{xyz}}{yze^{xyz}-2xz^3}  

d)

 xyexyz4yz33x2z22xz3yzexyz\frac{xye^{xyz}-4yz^3-3x^2z^2}{2xz^3-yze^{xyz}}  

7.

Partial derivatives graphically is define as

a)

A constant

b)

The 2D slope of the slice of a 3d graph

c)

The 3D derivative

d)

The derivative of the whole thing

8.

Which one of the following is always true?

a)

fxy=fxxf_{xy}=f_{xx}

b)

fxy=fyxf_{xy}=f_{yx}

c)

fxx=fyyf_{xx}=f_{yy}

d)

fxy=fyyf_{xy}=f_{yy}

9.

 f(x,y)=x32xy+3y2f\left(x,y\right)=x^3-2xy+3y^2   Which of the following is true?


a)

 fx=3x22y+y3; fy=6xf_x=3x^2-2y+y^3;\ f_y=6x  

b)

 fxx=6x; fxy=2+3y2f_{xx}=6x;\ f_{xy}=-2+3y^2  

c)

 fx=2x+6y+3xy2;fy=3x22y+y3f_x=-2x+6y+3xy^2;f_y=3x^2-2y+y^3  

d)

 fxx=6+6xy;fyy=6xf_{xx}=6+6xy;f_{yy}=6x  

10.

Find  fxf_x  and  fyf_y  from the equation  f(x,y)= ln(x2y3)f\left(x,y\right)=\ \ln\left(\sqrt{x^2y^3}\right)  

a)

 fx=1x       fy=32yf_x=\frac{1}{x}\ \ \ \ \ \ \ f_y=\frac{3}{2y}  

b)

 fx=1xy       fy=3x2yf_x=\frac{1}{xy}\ \ \ \ \ \ \ f_y=\frac{3x}{2y}  

c)

 fx=1x        fy=3x2f_x=\frac{1}{x}\ \ \ \ \ \ \ \ f_y=\frac{3x}{2}  

d)

 fx=x2y3     fy=3x22y3f_x=\frac{x^2}{y^3}\ \ \ \ \ f_y=\frac{3x^2}{2y^3}