What does the notation a1 represent?

a(1) is the first member of a sequence.

Step-by-step explanation:

"a1" could represent "a(1)," where a is the name of a sequence and 1 is the index of the first member of such sequence.  The second member would thus be a(2).

"a1" is not the equivalent of A-1 (which denotes something that's as good as it can get).

the 2 figures are congruent bc if you reflect abcd over the y axis then over the d axis the figures overlap

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