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In mathematical analysis, Clairaut's equation (or the Clairaut equation) is a differential equation of the form
where is continuously differentiable. It is a particular case of the Lagrange differential equation. It is named after the French mathematician Alexis Clairaut, who introduced it in 1734. [1]
To solve Clairaut's equation, one differentiates with respect to , yielding
so
Hence, either
or
In the former case, for some constant . Substituting this into the Clairaut's equation, one obtains the family of straight line functions given by
the so-called general solution of Clairaut's equation.
The latter case,
defines only one solution , the so-called singular solution , whose graph is the envelope of the graphs of the general solutions. The singular solution is usually represented using parametric notation, as , where .
The parametric description of the singular solution has the form
where is a parameter.
The following curves represent the solutions to two Clairaut's equations:
In each case, the general solutions are depicted in black while the singular solution is in violet.
By extension, a first-order partial differential equation of the form
is also known as Clairaut's equation. [2]