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08/17/11 - Differential Equation Models, Differentiation and Integration
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  | What is a differential equation?
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  | An equation containing derivatives (rates of change)
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  | What are differential equations used for?
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  | Modeling processes which involve rates of change so that we can successfully predict outcomes
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  | Example: A thermometer is placed in a glass of ice water and allowed to cool for an extended period of time. The thermometer is removed from the ice water and placed in a room having temperature 77°F. The rate at which the thermometer warms is proportional to the difference in the room temperature and the temperature of the thermometer.
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  | Physics and engineering are full of differential equations
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  | Malthusian model of exponential growth
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  | Logistic model of stable equilibrium
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  | What is the nature of the solution to a differential equation?
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  | It's a function which, when substituted into the differential equation, turns the differential equation into an identity.
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is the solution to the differential equation

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  | Differential equations which model physical phenomena:
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  | The phrase "y is proportional to x" implies that y changes in direct proportion to x, i.e., if x doubles, y doubles, if x triples, y triples. Functionally, this means y = kx, where k is a constant. In a similar manner, "y is proportional to the square of x" implies that y = kx2, "y is proportional to the product of x and z" implies y = kxz, and "y is inversely proportional to the cube of x" implies y = k/x3. For example, when Newton proposed that the force of gravitational attraction of one body to another is proportional to the product of the masses and inversely proportional to the square of the distance between them, he could immediately write:
 where G is the constant of proportionality, usually known as the universal gravitational constant. Use these ideas to model each of of the following situations with a differential equation. All rates are assumed to be with respect to time.
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  | The rate of growth of bacteria in a petri dish is proportional to the number of bacteria in the dish.
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  | A certain area can sustain a maximum population of 100 ferrets. The rate of growth of a population of ferrets in this area is proportional to the product of the population and the difference between the actual population and the maximum sustainable population.
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  | The rate of decay of a given radioactive substance is proportional to the amount of substance remaining.
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  | The rate of decay of a certain substance is inversely proportional to the amount of substance remaining.
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  | The voltage drop across an inductor is proportional to the rate at which the current is changing with respect to time.
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  | instantaneous rate of change of a function: y' = df/dt
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  | slope of the tangent line to a graph of the function at a particular point
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  | used in a linear approximation to a function: y = y(x0) + y'(x)(x-x0)
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  | limit of the difference quotient:

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  | Find the derivative of the following functions:
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  | Area under the graph of a function
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  | The derivatives in the following differential equations are functions of only the independent variable (x), so they can be solved by integration:
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  | Read Sections 1.1, 1.2 and 1.3.
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  | Do the exercises on p. 5 (2,6,8,9,10), p. 9 (2,4,6,8,10,12,13,15,16,18,21) and p. 14 (2,4,8,14,18,23,26,28).
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