Reduction: It means that the way to solve the problem is not direct, but to transform, transform, and turn it into a solved problem, or an easily solved problem, and then return to find the solution to the original problem. Which of the following does not belong to reduction? ['Xiao Zhang obtained the sum of the internal angles of the polygon by decomposing the polygon into several triangles.', "Xiao Wu was awkward with Xiao Wen. Xiao Wu wanted to apologize and couldn't let go, and told Xiao Cai the cause and effect. He asked Xiao Cai to explain to Xiao Wen. After Xiao Cai explained, Xiao Wu greeted Xiao Wen actively. People reconcile.", 'Xiao Li and Xiao Jiang have very different methods for solving the same type of problem. Xiao Li first studied special situations and finally solved general problems, while Xiao Jiang first solved general problems and then studied special situations.', 'Xiao Zhao adopted the principle of easy first and then difficult, and quickly completed a lot of physical assignments assigned by the teacher.']