It's just a way to confuse fish and pearls in our domestic teaching.
It is an opportunistic method to steal the first term of McLaughlin series and Taylor series.
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Because it doesn't have its own independent, self-consistent and complete theoretical system, it's just stealing.
Therefore, when using infinitesimal substitution with time equivalent, frequent mistakes are inevitable and inevitable.
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In order to prevent mistakes, we have added the clauses of self-mutilation, self-abuse and self-restraint:
You can't use equivalent infinitesimal substitution when there are addition and subtraction operations.
In fact, this sentence is overkill, a trick that there is no silver here, and a trick of people with a guilty conscience.
McLaughlin series and Taylor series are not limited to this, and they can be used in any way, such as addition, subtraction, multiplication and division, or in any combination.
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So, just remember:
When there are addition and subtraction operations, it is very cautious to use equivalent infinitesimal substitution, which is easy to make mistakes.
When there are addition and subtraction operations, the residual high-order infinitesimal may be eliminated.
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Although the self-harm clause arbitrarily excludes possible situations, it avoids too many mistakes.
I would rather not use it than be afraid of making mistakes. The essence is guilty and unconfident.
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When there are addition and subtraction operations, it is suggested that the landlord use Taylor expansion and McLaughlin expansion, which is foolproof.
Domestic teaching deliberately confuses Taylor series and McLaughlin series.
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