2:25 AM
C1, C2, C3.
C4, C5, C6.
C7, C8, C9.
@BillDubuque Reclosed and up for deletion.

10 hours later…
12:27 PM
@MartinSleziak Nobody objected, so I voted to close in the direction older $\to$ newer. We'll see from the review what others think about it.
This is again the situation where the older question is (by today's standards) PSQ and the newer shows some effort from the OP. 1734522: Find the solution of $\lfloor \sin^{-1}(x)\rfloor>\lfloor \cos^{-1}(x)\rfloor$ and 3478170: Value of $x$ in floor Inequality: $\lfloor \sin^{-1}(x)\rfloor >\lfloor \cos^{-1}(x)\rfloor$
I've seen the question in the close votes review queue, there are already some votes to close the new question as a duplicate of the older one.

2 hours later…
2:45 PM
[ SmokeDetector | MS ] Link at end of answer, pattern-matching website in answer, potentially bad keyword in answer (140): Combinatorial explanation for why $n^2 = {n \choose 2} + {n+1 \choose 2}$ by orla on math.SE

3:44 PM
[ SmokeDetector | MS ] Pattern-matching website in answer (79): Big Theta Notation! by jane909192 on math.SE

1 hour later…
4:56 PM
@user21820 Yes, thanks, but D1 still needs one more delete vote.

5:48 PM
Delete: DA, DB, DC, DD, DE, DF, DG, DH
Delete: DI, DJ, DK, DL, DM, DN, DO, DP