Question

I do not understand what subscript numbers mean

Answer 1

Answer:

  subscripts identify different instances of objects that have a similar meaning or definition

Step-by-step explanation:

You apparently are interested in the meaning of the subscript N in the explicit formula ...

  $A_N=\dfrac{7N}{N+5}$

Here, it is used to identify different terms of a sequence. When a value is substituted for N, it replaces all instances of N. Using your example, the first three values of $A_N$ are ...

  $\text{for N=1: }A_1=\dfrac{7\cdot 1}{1+5}=\dfrac{7}{6}\\\\\text{for N=2: }A_2=\dfrac{7\cdot 2}{2+5}=\dfrac{14}{7}=2\\\\\text{for N=3: }A_3=\dfrac{7\cdot 3}{3+5}=\dfrac{21}{8}$

So, if you're asked to find the 20th term of the sequence, you put 20 where N is, then do the arithmetic.

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Subscripts are also used to identify elements of a matrix or coordinates in multiple dimensions. For this purpose, there may be 2 (or more) subscripts, whose order has meaning. The subscripts 24, for example, in $A_{24}$ refer to row 2, column 4 of a matrix named A. That is, the subscripts are in row, column order.

In short, subscripts are used to identify different instances of similar objects.