I looked it up online, and this is the definition of substitution:
I think the most amazing thing about the substitution method is that it can simplify the calculation. For example, the original layer-by-layer operation is so complicated that it can't even be started directly. But after changing the elements, it becomes our common elementary arithmetic addition, subtraction, multiplication and division. method of substitution broke away from the limitation of linear thinking and made mathematics show artistic beauty.
From the point of view of simplification, substitution method is a simplification method, which simplifies the algebraic expression that cannot be processed into a familiar algebraic expression so that we can deal with it in the known field.
There is an article in Zhihu: Substitution Method: What has the RMB exchange changed? It's good. Interested friends can have a look. In fact, mathematics should be like this. The alternative method is a bridge between different fields of mathematics.
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