Could you tell me how to obtain the date of the day before the specified date? thank you!

Which expert can obtain the date method of the previous day of the specified date? thank you! Which of the following methods can be used to obtain the date of the specified date, instead of date (& quot; Y-m-d & quot;, strtotime (& quot; -5day & quot;), where "Y-m-d" is to be acquired by a daily master. Which of the following methods can you tell me how to obtain the date from the previous day of the specified date? thank you!
Which of the following methods can be used to obtain the date of a specified date, instead of date ("Y-m-d", strtotime ("-5 day ")), the "Y-m-d" must be replaced by a date value variable. Thank you !!!

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Do you mean that the star format is Y-m-d H: I: s, so you won't use date ("Y-m-d ", strtotime ("-5 day"). if so, format the preceding format using the time function. Use this function. I don't quite understand what the landlord means
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Date ("Y-m-d", strtotime ("-5 day "))
The first five days of today.

So
$ D = '2017-10-2 ';
Echo date ("Y-m-d", strtotime ("-5 day $ d "));

2010-09-27

5 days before?