# To estimate: The total personal income was rising in the year 1999. ### Single Variable Calculus: Concepts...

4th Edition
James Stewart
Publisher: Cengage Learning
ISBN: 9781337687805 ### Single Variable Calculus: Concepts...

4th Edition
James Stewart
Publisher: Cengage Learning
ISBN: 9781337687805

#### Solutions

Chapter 3.2, Problem 49E
To determine

## To estimate: The total personal income was rising in the year 1999.

Expert Solution

The total personal income was rising by about $1,627,415,600 per year in 1999. ### Explanation of Solution Derivative rule: Product Rule: ddx[f1(x)f2(x)]=f1(x)ddx[f2(x)]+f2(x)ddx[f1(x)] Calculation: Let x be the number of year, f(x) be the function of growth of population and g(x) be the function of growth of average income. f(x)=(Population increased per year)×(Number of years)+(Population in 1999)=(9200)×(x)+(961,400)=9200x+961,400 g(x)=(National average per year)×(Number of years)+(Average annual income per capita)=(1225)×(x)+(30,593)=1225x+30,593 Since the population was increasing at roughly 9200 per year and the average annual income was increasing at about$1400 per year, f(x)=9200 and g(x)=1400.

In 1999, f(0)=961,400, g(0)=30,593, f(0)=9200 and g(0)=1400.

Obtain the total personal income was rising in the year 1999.

Let F(x) be total personal income which is product of f(x) and g(x).

That is, F(x)=f(x)g(x).

Apply the product rule and simplify the terms,

F(x)=ddx(f(x)g(x))=f(x)ddx(g(x))+g(x)ddx(f(x))=f(x)g(x)+g(x)f(x)

Substitute 0 for x,

F(0)=f(0)g(0)+g(0)f(0)

Substitute the values f(0)=961,400, g(0)=30,593, f(0)=9200 and g(0)=1400,

F(0)=(9200(0)+961,400)1400+(1225(0)+30,593)9200=961,400×1400+30,593×9200=1,346,960,000+281,455,600=1,627,415,600

Therefore, the total personal income was rising by about $1,627,415,600 per year in 1999. To Explain: The meaning of each term in the product. In 1999, the term f(0)g(0)=$1,346,960,000 represents the portion of the rate of change of total income due to existing population’s increasing income.

In 1999, the term f(0)g(0)=\$281,455,600 represents the portion of the rate of change of total income due to increasing population.

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