y = 2x-1

First, we make a table of values for that equation:

x|1|2|3|4|5| 6|
y|1|3|5|7|9|11|

Look at the values of y.

To get from the 1st value of y, which is 1, to the 2nd value of y,
which is 3, we add 2

To get from the 2nd value of y, which is 3, to the 3rd value of y,
which is 5, we add 2

To get from the 3rd value of y, which is 5, to the 4th value of y,
which is 7, we add 2

So,

To get from the NOW value to the NEXT value, we always add 2.

We START at 1, and to get the next value, we add 2.

Some teachers like it written this way:

NEXT = NOW + 2  S.A. 1

where S.A. stands for "START AT"

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Other teachers like it written this way:

START = 1

NOW + 2 = NEXT.

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Edwin