Dlnx and dx have different meanings:

1 and dlnx mean to integrate the whole lnx.

1 and dx represent the integral X.

Integral is the core concept in calculus and mathematical analysis. Usually divided into definite integral and indefinite integral. Intuitively speaking, for a given positive real function, the definite integral in the real number interval can be understood as the area value (a definite real value) of the curve trapezoid surrounded by curves, lines and axes on the coordinate plane.

Extended data:

A function is said to be integrable if its integral exists and is finite. Generally speaking, the integrand function does not necessarily have only one variable, and the integral domain can also be a space with different dimensions, even an abstract space without intuitive geometric significance. As mentioned above, for the real function f with only one variable x, the integral of f on the closed interval [a, b] is written as follows:

over there

In addition to indicating that X is the variable to be integrated in F (integral variable), it can also indicate different meanings. In Riemann integral,

A mark representing a division interval; In Lebesgue integral, a measure is expressed; Or just an independent quantity (differential form). The integral in the general interval or integral range j, j can be written as

If there are multiple variables, such as in double integral, the function

The integral in area d is recorded as

or

In ...

Corresponding to the region d, it is the differential element in the corresponding integral domain.

References:

Baidu encyclopedia-integral