Docsity
Docsity

Prepare for your exams
Prepare for your exams

Study with the several resources on Docsity


Earn points to download
Earn points to download

Earn points by helping other students or get them with a premium plan


Guidelines and tips
Guidelines and tips

Implicit Differentiation or Related Rates - Study Guide | MTH 251, Quizzes of Calculus

Material Type: Quiz; Class: Calculus I; Subject: Math; University: Portland Community College; Term: Unknown 1989;

Typology: Quizzes

Pre 2010

Uploaded on 08/18/2009

koofers-user-81q
koofers-user-81q 🇺🇸

10 documents

1 / 10

Toggle sidebar

This page cannot be seen from the preview

Don't miss anything!

bg1
Mr. Simonds MTH 251 - Implicit Differentiation/Related Rates
Page 1 of 10
Introduction to Implicit Differentiation
Find the formula for the first derivative of the function
2
18yx=−
two ways.
1. Use
Explicit
Differentiation. (i.e. differentiate the explicitly stated function.)
2. Use
Implicit Differentiation
. (i.e., differentiate the implicit equation
22
18.xy+=
)
Figure 1
pf3
pf4
pf5
pf8
pf9
pfa

Partial preview of the text

Download Implicit Differentiation or Related Rates - Study Guide | MTH 251 and more Quizzes Calculus in PDF only on Docsity!

Introduction to Implicit Differentiation

Find the formula for the first derivative of the function y = 18 − x^2 two ways.

1. UseExplicit Differentiation. (i.e. differentiate the explicitly stated function.)

2. UseImplicit Differentiation. (i.e., differentiate the implicit equation x^2 + y^2 = 18.)

Figure 1

Introduction to the classic implicit differentiation strategy

Find the slope of the curve in Figure 2 at the point ( 1 , 1 ). The equation used to graph the curve was

y^5^ + 3 x^3 y^2 + 5 x^4 = 9.

1) Differentiate both sides of the equation with respect to x.

  • Remember to treat y as a function of x and use the chain rule. For example:

dx

dy

y y

dx

d

  1. Algebraically solve for

dx

dy

3) Replace x and y with their values.

Figure 2

Introduction to Related Rates

Suppose that the lengths of the two sides of a rectangle are defined to be x and y with each

length measured in cm. Suppose that at an arbitrary time designated as t = 0 , the side associated

with x has a length of 5 m and the side associated with y has a length of 8 m. Suppose further

that each side of the rectangle grows at the constant rate of 2 m/s. Does it follow that the area of the rectangle grows at a constant rate?

Approach 1: Find formulas for x and y in terms of t where t is the number of seconds that have

passed since the rectangle was 5 m × 8 m. State and differentiate the area formula

in terms of t.

Approach 2: Redefine x and y to be the lengths of the sides t seconds after the rectangle was 5

m × 8 m. Differentiate the area equation A = x y with respect to t.

Introduction to the classic related rates problem solving strategy Sue Bob is one tall gal – 6 foot to be exact. Sue Bob is running towards a street light post; the lamp on the post is 40 ft above ground. The lamp is bright enough and the night is dark enough that Sue Bob casts a shadow behind her as she runs. When Sue Bob is exactly 30 feet from the base of the street light, she is running at exactly 10 ft/s. At what rate is the length of Sue Bob’s shadow changing at this instant? Is the shadow getting longer or shorter?

Agenda 1 : What are our variables? Please note that we are given the value of exactly one rate in this problem, so we need exactly 2 variables; one variable that differentiates to the given rate and one variable that differentiates to the asked for rate. Carefully define each variable (including the time variable). Make sure that you include correct units in your definitions. Angles

must always be defined with a unit of radians.

Agenda 2 : What is our relation equation? A diagram of the problem situation with the variable pieces labeled as variables and constant pieces labeled with their constant values is usually helpful with this agenda.

Agenda 3 : What is our rate equation? This is derived by differentiating both sides of the relation equation with respect to time.

Agenda 4 : Account for each variable and each rate in the rate equation. We are interested in what is happening at one specific instant; state the values of each rate and variable at this

instant (except, of course, the unknown rate). Make sure that you state negative rates for

pieces that are getting smaller over time.

Agenda 5 : Plug the known values and rates into the rate equation and solve for the unknown rate.

Agenda 6 : State a contextual conclusion that includes the rate unit. Make sure that your conclusion clearly communicates whether the object is increasing or decreasing.

Another example of the classic related rates problem solving strategy

At noon one day a truck is 250 miles due east of a car. The truck is travelling west at a constant speed of 25 mph and the car is travelling due north at a constant speed of 50 mph. At what rate is the distance between the two vehicles changing 15 minutes after noon?

Agenda 1 : What are our variables? Please note that we are given the value of exactly two rates in this problem, so we need exactly 3 variables; two variables that differentiate to the given rates and one variable that differentiates to the asked for rate. Carefully define each variable (including the time variable). Make sure that you include correct units in your definitions. Angles

must always be defined with a unit of radians.

Agenda 2 : What is our relation equation? A diagram of the problem situation with the variable pieces labeled as variables and constant pieces labeled with their constant values is usually helpful with this agenda.

Agenda 3 : What is our rate equation? This is derived by differentiating both sides of the relation equation with respect to time.

Agenda 4 : Account for each variable and each rate in the rate equation. We are interested in what is happening at one specific instant; state the values of each rate and variable at this

instant (except, of course, the unknown rate). Make sure that you state negative rates for

pieces that are getting smaller over time.

Agenda 5 : Plug the known values and rates into the rate equation and solve for the unknown rate.

Agenda 6 : State a contextual conclusion that includes the rate unit. Make sure that your conclusion clearly communicates whether the object is increasing or decreasing.

A tank filled with water is in the shape of an inverted cone 20 feet high with a circular base (on top) whose radius is 5 feet. Water is running out the bottom of the tank at the constant rate of 2 ft^3 /min. How fast is the water level falling when the water is 8 feet deep?