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implicit and explicit solution of differential equation lecture 4
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FAMILIES OF SOLUTIONS The study of differential equations is similar to that of integral calculus. In some texts a solution is sometimes referred to as an integral of the equation, and its graph is called an integral curve. When evaluating an antiderivative or indefinite integral in calculus, we use a single constant c of integration. Analogously, when solving a first-order differential equation F(x, y, y) 0, we usually obtain a solution containing a single arbitrary constant or parameter c. A solution containing an arbitrary constant represents a set G(x, y, c) 0 of solutions called a one-parameter family of solutions. When solving an nth-order differential equation F(x, y, y,...,y(n)) 0, we seek an n-parameter family of solutions G(x, y, c1, c2, . . . , cn) 0. This means that a single differential equation can possess an infinite number of solutions corresponding to the unlimited number of choices for the parameter(s). A solution of a differential equation that is free of arbitrary parameters is called a particular solution. For example, the one-parameter family y cx x cos x is an explicit solution of the linear first-order equation xyy x2 sin xon the interval (
,
). (Verify.) Figure 1.1.3, obtained by using graphing software, shows the graphs of some of the solutions in this family. The solution y x cos x, the blue curve in the figure, is a particular solution corresponding to c 0. Similarly, on the interval (
,
),y c1ex c2xex is a two-parameter family of solutions of the linear second-order equation y 2yy 0 in Example 1. (Verify.) Some particular solutions of the equation are the trivial solution y 0 (c1 c2 0), y xex (c1 0, c2 1), y 5ex 2xex (c1 5, c2 2), and so on.
,
). (Verify.) Figure 1.1.3, obtained by using graphing software, shows the graphs of some of the solutions in this family. The solution y x cos x, the blue curve in the figure, is a particular solution corresponding to c 0. Similarly, on the interval (
,
),y c1ex c2xex is a two-parameter family of solutions of the linear second-order equation y 2yy 0 in Example 1. (Verify.) Some particular solutions of the equation are the trivial solution y 0 (c1 c2 0), y xex (c1 0, c2 1), y 5ex 2xex (c1 5, c2 2), and so on.
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