With variable substitution,several kinds of linear differential equations are solved and several sufficient and necessary conditions are obtained.

The method searching for solutions to first order non liner equation with variable substitution and integral gene, and the method searching for solutions to all the integral with integral gene were discussed and expounded in this paper.

This paper uses variable substitution to discuss the methods of solving three integral kinds of function-coefficient differential equations of the third order.

With proper method of variable substitution, the soluble method to two kinds of inegrable equation of Riccati form is found, and the general integral expressions are given.

In this paper,we discuss and obtain an analytic intuitionistic proof method of the variables chang formula in double integrals and give a simple proof method.

This paper studies the problem of the solution to the unlimited optimization of quadratic differentiable function f(X)by means of variable transformation, presents a characteristic value method, and solves the direction of search when Hesse matrix is non-definite,The calculations show that the algorithm is satisfactory in both the number of interatives and the stability of the numerical value.

This paper gives the general solutions of the six order inhomogeneous linear differential equation with variable coefficients,by the method of the variable transformation.