Respuesta :

meerkat18
The first thing to know is that "an" and "a1" are names with subscripts and are and different from multiplication.
 an = a1 + (n-1) d
 add -a1 to both sides
 an - a1 = a1 - a1 + (n-1) d
an - a1 = (n-1) d
d = (an-a1)/(n-1)

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