∴(a3+a6)-(a2+a5)
=a3+a6-a2-a5
=2d
=-30-(-22)
=-8
That is, d=-4.
Then a2+a5 = 2a1+5d = 2a1-20 =-22.
Solution: a 1=- 1
The general formula of the sequence an is:
an=a 1+(n- 1)d
=- 1+(n- 1)*(-4)
=-4n+3
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