What is called a differential equation?

The question asks to define a differential equation. Let's analyze the options provided:

1. Уравнение с неизвестной функцией (Equation with an unknown function): This is too general. Many types of equations involve unknown functions, not specifically differential equations.
2. Уравнение, содержащее производные неизвестной функции (Equation containing derivatives of an unknown function): This definition accurately describes a differential equation. The presence of derivatives is the defining characteristic.
3. Уравнение с параметром (Equation with a parameter): An equation with a parameter might be a differential equation, but the parameter itself is not the defining feature of a differential equation.
4. Система линейных уравнений (System of linear equations): This refers to a set of simultaneous linear equations, which are algebraic, not differential.

Therefore, the most accurate definition is an equation that contains derivatives of an unknown function.

Ответ: Уравнение, содержащее производные неизвестной функции