RQS@ @pþÝn¾aì@pbÉibnn¾a ()
a2011 a4 = a3 + d = a1 + 3d .
an = a1 + (n − 1)d
2, 9, 16, 23, 30, …
9 − 2 = 16 − 9 = 23 − 16 = 30 − 23 = 7
.d = 7 a1 = 2
. a2011 = a1 + 2010d = 2 + 2010 × 7 = 14072
a,b,c
b −a = c −b
2b = a + c
b = a +c
2
(arithmetic mean)
.
3k + 1, k, − 3 ()
.k